Tauren Summoner:
the Tauren summoner summons many Powerful units. Allthough the ability to summon Taurens off the bat may seem ridiculus, the taurens in this game are quite balanced even though still a powerful unit. The Tauren summoner also uses War Stomp, which does less damage and doesnt stun for as long as Storm Bolt, but War Stomp affects all enemies around the Tauren summoner, not just one target.
Tauren:
One of the neat things about taurens is there ability to Pulverize, dealing 60 damage in an AoE by chance. they do roughly 28 damage but they have a long cooldown of 2.3 so they wont attack as fast.
Spirit Walker:
with close to 22 damage, they are very effective against units with Heavy or Small armor. they can turn etheral which is neat if the enemy isnt using many units with Magic attacks.
Kodo Beast:
Although they are your third summon, they only do 24 damage. however, they also have command aura which makes up for this lesser damage. they also do not have much armor, but they make up for it in hit points. try and keep these away from groups of spellcasters.
Mini Chieftain:
they have only 2 armor, which isnt much compared to most summons that require level 8, but when fully upgraded with the Steel Armor upgrade they are a force to reckon with because they will have 8 heavy armor and 1500 health. they also have pulverize.

Dwarf Summoner:
a nice feature about the dwarf summoner is the Storm Bolt which is VERY annoying to enemy heroes at the very start of the game. say the game just started and you begain to charge into the enemy base. odds are an emey hero will be doing the same thing, so storm bolt it before it can do anything, then while its still stunned, get a group of 5 riflement to gether and then you get first blood assuming that the fight does not transpire next to enemy towers.
Rifleman:
basic ranged units that have 3 armor and are quite effective against air units(not as much as flying machines though) and they start with 600 range. if yuo find the enmy is using Chimeras and faerie dragons(or dragons in general) then go with Flying Machiens instead.
Flying machines:
good anti-air with RANGE and SPLASH. it also very indestructible in very early game because it has 5 armor.
Mortar Teams:
The answer to towers and the odd Pocket-Factory that a Car Summoner might throw at you. if you research Fragmentation Shards for them, they are especialy effective agaiinst summons with Unarmored and Medium armored units. Notice anything about the night elf summons? they have THOSE types of armor! however even with 3 armor, they still get beaten by Spellcasters and magic attacks. also, if the enmy is using sorceresses, they can cast invisability on their own spellcasters and then the mortar teams will really get pummeled.
Gryphon Rider:
they only have 3 armor, which isnt much in late-game. they do more damage to ground then to air, but they do splash against air. they turn into very powerful killing machiens when you fully upgrade Iron Forged Swords.

Orc Summoner:
a ranged summoner that can cast Feral Spirit whenever needed. say its early game, and you're busy waiting for your Orc or Shaman spell to finish its cooldown, Feral spirit is good to fill up the time to give you additional summons. Feral Spirit sucks in mid and late game.
Grunts:
Grunts are great first-choice summons because in an early rush, you can pillage enemy towers for lots of gold! they also have 3 armor.
Shaman:
Shamans are terrible for rushing into the base, the arcane towers will drain their mana and kill them in an instant. they are effective against units with Heavy and Small armor.
Raider:
Raiders, like Grunts can also pillage, but they also have Ensnare! they only have 1 armor, so its good idea to upgrade their armor to make them more cost-effective. they are quite addept at destroying towers. keep that in mind.
Wind Riders:
wind riders have envenomed spears, which adds poison to their attack! they have 4 armor and roughly 70 damage. there are upgrades available for their attack and armor to make things easier.

Draenei Summoner:
this summoner is quite unique as it has units with magic sentry(if upgraded). this summoner can also cast Shadow Strike for 40 mana dealing 50 damage and then 10 every few seconds.
Draenei Darkslayer:
a basic unit with immolation. these are quite useful if you find the enemy to be using lots of melee(such as bears, grunts, footmen, etc.)
Draenei Disciple:
this unit is a very good healer and when you're up against things like Doom Guards, infernals or knights, you'll find that having a few of these around to support allied summons saves lots of mana(and cooldown time).
Draenei Harbringer:
main spellcaster draenei with Bloodlust and Ray of disruption, which is like chain lightning but instead of doing damage, it removes buffs. have less hit points then most other level-3 summons, but are quite effective from far away and are very good when used to "kite"
Draenei Seer:
has the most armor out of all draenei summons, however has the same hit points as most level-3 summons. does the most damage out of all draenei. has very awsome abilitys like Slow, brilliance aura and healing wave.

Human Summoner:
the human summoner is a very well balanced summoner with Brilliance Aura, which is great if your allies are picking summoners that use lots of mana such as "arrow" abilities and immolation.
Footman:
this unit is VERY effective if your enemies are picking ranged summons because it has defend. it also has the suprising armor of 5. however, they're a terrible idea to use when the enemy is using air.
Medivh:
the only ranged unit of the Humans. can go into Hawk Form, which is quite good if the enemys are using Melee summons. however, hawk form is a terrible waist of summons, mana, and time if the enemy is using anti-air summons like Hippogryphs, Flying machines and most dragons.
Knight:
Knights are quite powerful against most attacks. but against spells and summons with magic attacks, they are just an awful waist of 150 mana.(thats LOTS in early game)
Super Militia:
these Pumped-Up militias have 4 armor, and roughly 83 damage. with about 1000 health, they are very good tanks.

Blood Elf Summoner:
if you like annoying the enemy(even just a little) then this a good summoner for you. most things he summmons use a variaty of good spells and starts with Siphon mana, which steals mana. this spell is quite effective when teamed with sorceresses to slow the target and then siphon mana him. if the target is a higher level, you get that much more mana and higher level is not good if you have no mana to do anything.
Blood Elf Archer:
this is the only blood elf summon that doesn't use summons. very good with kiting tactics and makes use of the Strength of the Moon upgrade as well as marksmenship.
Blood Elf Sorceress:
another spellcaster adept at harrasing the enemy. they move fairly fast which is good if you need to get to places quickly. they have slow, which esspecialy effective when teamed with the summoner's Siphon Mana. if the enemy has a very good summon thats attacking you, use polymorph! you can also use Invisability to sneak good summons behind enemy lines to attack the book of summoning and win! of course, you have to get rid of an Arcane tower first.
Spell Breaker:
a spell caster with 4 armor. its pretty much the anti-spellcaster unit with Spell Steal, spell immunity, control magic and feedback.
Dragonhawk Rider: the odds are that Cloud won't really be all that useful when you're able to get this summon because most towers will have been destroyed. but the Dragonhawk rider is a very good anti-air kiling machine when you use its Aerial shackles ability against powerful air units. it can make use of the Iron Forged Swords upgrade and has 4 armor.

High Elf Summoner:
the High Elf Summoner is simmaler to the blood elf summoner since it has sorceresses. Sylvanas, the high elf summoner has trueshot aura, which is quite effective when your allies are using plenty of ranged summons.
Sorceress:
Exactly the same as the Blood Elf Sorceress
Priest:
these are excelent healers with Heal, Inner fire, and dispel magic which EXTREMELY effective in early and mid game stages against summons.
Swordsman:
18 damage, 3 armor and 420 hit points with the defend ability.
Dragon Hawk:
although it may seem simmaler to the Dragonhawk Rider, they are quite diffrent from eachother. Dragon Hawks, have the ability to Ensnare other units and do around 70 damage. they only have 1 small armor, so try to keep them away from groups of enemy spellcasters.