Freshwater defenatly!!! as far as getting colorful fish, i had alot of fun with chiclids (sp?...been a while) they are beautiful fish and grow to be a nice size in a nice tank. they are easy to keep, and will interact with you as you look into their world on the other side of the glass.
there are two kinds, african, and south african. you arent supposed to mix the two in the same tank, but i did without much problem. they can also be fed live feeder guppies, instead of dry food, but i would only do that on occasion.
aquariums are very cool and calming. good luck with it.