I have went the 3 gallon route before, and honestly, it's just as expensive to set up the three gallon as it is the ten gallon, but the ten gallon is less of a headache. The evaporation rate was ridiculous with my 3 gallon pico, but with my ten gallon it only goes down about a 1/4 of an inch every day. Also its easier in a ten gallon to hide all the ugly stuff, such as the heater and power head(s). If you have some
DIY skills, its really easy to add an in tank overflow
sump which has really stabilized my tank. My 3 gallon tank i tried almost a year ago crashed and burned, so i tried it again with a ten gallon, and its so much easier.