I suppose if I had to pick a actual species, I would also say Caitians. The problem is Trek tends to a good job with their species. Even species like the Cardassians and Changelings, which are mostly inclined to be seen as a "Villianous" species are fairly fleshed out to the point where, even if you aren't rooting for them, you like them anyways.
Caitians and your generic aliens just haven't been given the fleshing out and backstories needed to make them lovable. Caitians just seemed be thrown in there cause they could, and well lets be honest, there is a reason generic aliens are called "generic" they aren't suppose to be fleshed out, they are just out there to be there.