Yeah I usually play as a human. Mostly because I prefer the human portraits and bodies I've found in the art packs so far. I think purely based on stats I would be more likely to play as maybe a Dragonkin or a Drow but I don't like the art I've found for either of those races so far. I could just use art from another race instead I guess but have been too lazy to so far.
I guess that's actually a bit of a hidden advantage for humans that many might not think about though. Humans can breed with several of the other races without needing them to have the breed sow perk so having the main character's stats boosted guarantees that your kids will have good stats even if you breed with a slave that has stats that are mediocre.
The only reason I generally need to even visit the slave markets is to complete a servant quest in the first week or to buy a slave of a specific race later on if I want one. I get plenty of kids to never need to buy any slaves for the entire game, although I would still get Daisy. I actually don't buy any slaves from the slave market to keep unless I want a specific race.
So the method I mentioned works fine for any race, you just have to rely exclusively on kids from your initial slave if you don't go the breed sow route. I've played as Drow or Dragonkin before and just wind up with nothing but my own race for slaves with the exception of Daisy.
Humans and Kobolds are good collectors for all kinds of metalls and woods... even bones and stuff but they aren't that good in combat, crafting or being charming.
Drows/Dark Elves are the Best Magicians, Dragonkin are the best "Normal" Fighters, Harpies are the Best Administrators...
In the Late game the race specific Bonusses make the greatest difference and can influence your play style quiet a bit.
Slaves get Malus on crafting skills but Bonusses on gathering skills, so Humans and Kobolds are best as slaves, Dwarfs (Smith) are better of as Peon or something better once included.
Nereid grants a bonus on Fishing, Wolf girls on hunting (meat and leather) and Dryads on farming and Bunnys as whores (only useful at the very beginning, but daisy will only unlock that option later when her loyality is high enough) which makes them good slaves
Maybe Arachnes will get a Race Bonus on Tailoring and in Part 1 Scylla's got a Bonus on cooking again Peon or better.
The great fun was always to have a menagere of Monster girls in order to get the best results, even if all slaves have maxed abilities... but that's my personal opinion