what would be a better Macro tank a 20L or 29

[Gunbeaux]

I have the 20L set up at this time but got a few extra tanks when the Petco $1 gail was on. Was thinking of using the 29 with the 20L as a sump. but have an extra 20L if i need it. Also got a 40B and 55 for some future projects. don't have the space to set them up right now or the lighting etc. the 55 is geing donated to the local school this fall. thanks for the input..... the FTS of the 20L is about 2 months old. I also have a 10L pic included