Those on other nano-type boards/forums seem to set 20g as the upper spec limit for these tanks, with a 3-tang maximum.
If I didn't have a 15 tall, I would DEFINITELY want a 20 gallon. I just took down a 10g nano tonight to make room for a bigger tank. There just isn't enought volume in a ten, IMHO and IME.
I really like the 15 tall though. It looks amazing where the TV used to be, and has a similar "screen size." The vertical aquascaping options and challenges are stimulating and rewarding.
Of course, remember I'm still fairly new at all of this - I'm easily impressed. Best times are sitting with my 9-yr-old, faces pinned to the glass.
Cheers,
Aj
