well, i know most of mine were happier when they were upgraded to larger tanks. Cup's alot more active now, even with his longer fins, than he was in his one gallon tank. same with Freya, a CT female who passed away Halloween weekend. she went from a .5, up to a 2.5, and was really happy about the space. she'd explore for hours, finding new things that she'd get excited about. only betta i've ever had who DIDN'T like more space, is Lulu. she's honestly happier in her 1 gallon, than she was in a 2.5 gallon. if i ever get the chance to do my dream tanks(two 20 gallons, divided 4 ways), i'll try her out in a '5', but if she doesn't like it, she'll stay in a 1, with daily water changes.