Best thing is to think about what your tank is like now and what you want it to be in the future and then use that to research, research, research a particular pleco.
for example...perhaps you would like to have a nice planted tank which is fine but there's nothing like a large horse destroying your plantings when you are just getting started with a foreground later on. If you don't have another tank for your pleco while this foreground roots you are not good.
hope this helps...
Trinidad pleco or common pleco according to what most LFS sell, should be only sold to seasoned aquarium owners.