woodstock
Fishaholic
Go with your average rectangular tank. Glass is the best. I heard some heaters can't be used in plastic/acrylic tanks. Plus, if you go with the larger (5 or 5.5...I have a 5.5 gallon) it will allow you to add a snail or a couple shrimp later on. Trust me. Once you get a tank you are going to want to spiff it up with a little something new here and there and the larger it is, the more satisfied you will be. Gives you more options.
Sorry, but I'm pretty curious as to why heaters can't be used with acrylic tanks?
And I believe that as long as the heater doesn't actually touch the actual tank (plastic/acrylic), it should be okay. A little risky, but just FYI.