I also have a 17L plastic tank but that's kept for emergencies(I'm paranoid that one of the tanks will crack, or get smashed by my toddler).
I'm on the lookout for something between 240L - 350L to upgrade the goldfish, well I'll probably move the goldfish into the 240L and the tropicals into the new tank if it's bigger then what they have now. I'm hoping when we move that we'll have a decent sized dining room that I can fill with tanks!
3 tanks- 10 gallon community tank, 2 one gallon betta bowls, wish I could get a 20 gallon, maybe in April, don't know for sure now. If I get a 20 gallon I'll move my fish in there, get more platies, more guppies, use the 10 gallon as a sorority tank. But those are just dreams