The best size tank is the one you can be happiest with and maintain for the longest time. I know that sounds cliche, and possibly not very helpful, but I don't think what works for me, or post number six, or eight, or twelve (picked you all at random, sorr!), etc. is necessarily going to be best for you. In tanks over 90g I think 120 and 150 are the most popular. If I had to guess why, this would be that tanks larger than that start to get cost and space prohibitive in the sense of shipping, storage, placement in your home, office, etc.