What's is everybody's favorite tank sizes? 5 gal? 20? 50? Others?
I have been active in this hobby for 30 years now, and in that time have had many tanks of differing sizes depending upon the space I had available. The largest was my 5-foot 115g Amazon riverscape, the smallest a 10g (now being used as a QT for new fish acquisitions). With tanks of 90g, 70g, 55g, 40g, 33g, 29g, and 20g. When I moved from my house this past May into a Townhouse I downsized the tanks due to a much smaller fish room now from what I had at the house with all those tanks. Not everyone has a dedicated room, nor in fact space for larger tanks. So to answer your question, I have found my 40g and 29g to be very versatile tanks and these are my favourites. You can create a lovely aquascape in either of these. The 29g I like because it has the length of a 20g long but with the added height which does make it much more workable. And the 40g has the additional width front to back (18 inches compared to 12 inches for most smaller tanks) which makes a huge difference in a 3-foot length tank. My 33g is 3 feeet but only 12 inches wide and is considerably less workable.
I have to hear about this 115g Amazon tank. Sounds amazing.
I acquired this tank in 1996, and when it got to be 20 years old in 2016 I decided to get rid of it because I was frankly worried about leaks with a 20-year old tank on a concrete floor but one without any drain; I lay awake nights imagining the centre brace giving way and a major flood! I have photos of some of the displays I had in this tank durng the last decade when I had a camera, though not a very good one.