Cue cute car commercial: "Wider is better"
I would go with either the 65g or 75g, depending on the type of fish you intend to house. The 75g is a great size for schooling fish: 48"x18"x20". The 65g is a better size for tall fish, such as silver dollars or angelfish:36"x18"x24"
Always try to get the biggest footprint you can, but remember that depth is important. There's no point in getting a tank if your fish can't turn around in it.
The 55g is only 13" deep. That pretty much limits you in what you can put in it. Certainly not any fish that grows more than 8", they won't be comfortable and some won't be able to turn around.
Roan
I would go with either the 65g or 75g, depending on the type of fish you intend to house. The 75g is a great size for schooling fish: 48"x18"x20". The 65g is a better size for tall fish, such as silver dollars or angelfish:36"x18"x24"
Always try to get the biggest footprint you can, but remember that depth is important. There's no point in getting a tank if your fish can't turn around in it.
The 55g is only 13" deep. That pretty much limits you in what you can put in it. Certainly not any fish that grows more than 8", they won't be comfortable and some won't be able to turn around.
Roan