Since I like to play long games...
In vanilla Moo2 I like the non-repulsive lizards, as they give me good trade money early on and big sized fleets to combat later in the game.
Also Psilons can be a good opponent on later game if you manage to help them and make them grown (I always try to be the Psilon's bodyguard).
On a roleplay aspect, I love the Gnolls (Star Trek Ferengis) and the Coids
(Star Trek Sheliak)

Darlocks are the one I most hate in vanilla, they frame you, distrupting your trades, and you cannot see their fleets coming. They are always the first I want to eradicate.
On your ICE mod, I really like the Birds. They are friendly and nice on early game, and later, when you fight them (t200+), their fleets are usually a good challenge
with a good tech level.
On the roleplay aspect, I like the Bears, when they threat me, I can finally take them
seriously, unlike in the vanilla game

The one I hate in ICE are the Ants. If they start near my home, I'm toasted, I can as well restart another play. And they are very, very difficult to keep friendly, since they are often (or always?) Xenophobes. If this was not enough, in late game, being them uncreative, their huge fleets are composed of tin cans, not a challenge at all. Not fun at start game, not fun at end game, only good at mid game.
In general, I like all the ICE races but the Ants.