Here's what I did in my campaign:
Gnoll are your native stand-ins. They were there first and the humans pushed them off the land. Yet still, they worship a very real and nasty god, take slaves, and skin humans for their pelts. If they had it their way, they'd eat all us peoples that they see as cattle. They are convinced they're the Master Race.
Goblins are fey. They are agents of pure chaos that bubble up out of the deepest earth. No goblin babies, no hope of redemption---they are the Jokers to the world's Batmen. They just want to see it all in flames and couldn't care less if that means they burn too because they are will just eventually be reborn from the earth's womb in another time or place. It's all wicked good fun to them. A counter-balancing force of nature to the elves and such.
Orcs are mules---the result of goblins that mated with the animals of the natural world (ape, pig, human, etc.). The muscle. No females. No babies. Orcs that come from goblin+humans make the best soldiers for ye old dark army. A goblin can be male or female as needed and can cross-breed with just about anything, including other fey...like leprechauns. There are no half-orcs, just a wide variety. If you got a little orc, then you are an orc---and you won't be having kids. You are subhuman intelligence and filled with a bit of lust for making things blow up.
Bugbears are goblins+bears+goblins+bears+stuff, but breed true---animal intelligence.
Hobgoblins all come from oversea, and are the most humanoid and civilized. They worship the Art of War.