limit to picking 3 favorite races, id say mine are the Dwarf, Dark Dwarf, and the Minotaur

In WBC2 it was the high / wood elves easily. Once you got your army of ancient wisps and elcors balm, your hero was almost unbeatable due to the fast healing, and your Titan was game over for everyone else.
WBC3 has reduced the effectiveness of that, but Wood elves still rock. After that I'd say Humans (lvl 4 generals, and good all rounders), and Daemons.

My favorite were the Fey, who always had an underdog feel to the tall races, they had a lot of upgrades also and I felt their towers were always the most damaging (maybe because it was magic damage not the usual piercing, also you'd turn to crystal on death)

The Daemons, the Minotaurs, and the Snake people are my favorites. All of them were really strong.

Daemons, Lizardmen, Dark Elves

I'm going to go with Lizardmen.

I'm doing the campaign with them at the moment, I have a lv 18 Healer with high Chr (so I can deploy at least 2 naga at the start of every mission). My friends call him Raptor Jesus.

Minotaur by a huge lead, followed by Dark Elves.
I've always been a fan of Minotaurs in any game where they were available, and they kick ass in here to boot (DRUNKEN BURNING MINOTAURS OH LAWD)
The Dark Elves just have style, and a good firing line of their sorcerers just spells death for most things I've encountered.

Raptor Jesus, are you Matt?

Hmmm I would say my three favorites are Barbarians, Plaguelords, and Swarm.

Minotaurs - eating animals to heal, aformentioned burning drunken beserkers, simple to build when im lazy - My minotaur alchemist had the mix of mercantile and mucle to win fast - barbarians led by my minotaur work well - simular but lazier to win

Empire elephants and archers seem to handle most anything - best choice of wizards, i just allied with dark elves in the campaign and use their mercenaries to compliement troops with spiders swarms from enamies dead -

I like demons but a mana drought and some enamies are a bit tough to handle at times
summoned labourers being temporary is a major change fro v2 where i woud summon labourers for mines - now doesnt work

I love this game, I haven't played it in years!

My favourite are the Fae. I think they were my favourite because I was little when I first played the game, and they are the most girliest things around. I loved them! I didn't like them for any strategy plan, just because they sounded cute and looked cute. Still my favourite today of course.

I sort of liked the Barbarians too. I always liked barbarian stuff and movies, so I liked them only for that. I did play them a few times on skirmish maps.

Minotaurs for me, Followed by Undead, and my third used to be Empire, but now it's Knights.

I can't figure out how to use any unit other than Minotaur King as Minotaurs, though :/

Mine are...in no particular order

Plaguelords...amazingly fun race. My guy is a Plaguelord Archmage. I love the looks of the buildings and towers, too. And that Fire spore is really powerful. More of an offensive style race, get a lot of damage+ research.

Dark Dwarves is another fun one. I really enjoy a Dark Dwarf Tinker, get more powerful buildings and what not and I made my guy a fighter. Kind of a slow race,more defensive.

Fey are a funny race. Its hilarious to see tiny people attacking dinosaurs or other giant enemies. The voices are fun too :D I made mine a Fey merchant, not the most exciting hero, but I get cheap units.

And runner ups go with Undead, but I never play one, seems too common. Dwarf is fun, but I prefer Dark Dwarves. And I like Swarm, mostly because I love insects and it has...ANTS! :D. Haven't found a hero I liked though, for Swarm.

From a defensive-player/turtler perspective:

#1 - Fey army with a Dwarf Tinker hero

Fey towers have magic damage -- easy (no hassle) to deal with skeletons early on.
Fey towers are small (only 2x2 squares) -- lets you pack more into the same area.
Fey towers generate crystal -- the more they attack you, the richer you get.
Tinker gets Engineeer skill -- think Fey towers with 1000+ hp each.
Dwarf gets Rune Magic -- think Fey towers with 1000+ hp each and a hero beind then casting Earthpower.
Tinker gets alchemy -- for converting that crystal into whatever is needed.
Leprechauns -- tower stuffers that produce gold.
Unicorns -- healing (mainly for healing Pegasus early/mid-game and Celestial Dragons late game)

Toughest fight for Fey: Dark Dwarves (before the Dwarf Tinker has enough levels to be really useful -- can stay tough until you have multiple Celestial Dragons and Unicorns, and sometimes even then)

#2 - Wood-Elf army with High-Elf Healer hero

Ancient wisp "farms" -- crystal generation and lots of fire power (and Healer hero to (try to) keep them alive) -- front-line fighters early game, tower support mid/late game.
Magic wells -- gold generation, good way to boost army points.
White trees -- another (very dense -- 3x1 squares) way to boost army points and raise titan-killing armies in seconds. (Both magic wells and white trees are good for turtling -- eventually replace walls outside of towers with magic wells for more gold income.)
Healing + Elcor's Aura + Elcor's Balm + Celestial Dragons = game over

Toughest late-game fight for Wood-Elves: High-Elves (Ice Maidens and manticores can do a lot of damage fast, and the freezing slows down your response)

#3 - no clear choice -- either High-Elves or Empire -- say Empire with a High-Elf Merchant

Can start out a bit rough.
Improves once you can put Halberdier in towers.
(Can instead degrade from "rough" to "disaster" if you don't have a hero with trade or transmute, and can be much harder than necessary if you don't have a hero that can produce resources.)
Improves more once you can start adding one white wizard to each tower for magic damage.
White wizards -- healing.