, but I've had several different sized tanks in the last decade or thereabouts. These have included a 75g, 55g, 125g, and 180g, and other, smaller tanks.
I would *far* prefer the 120g to the 125g. It is only 4 feet long (less lighting expense), but most importantly, I would never return to anything less than a 24" front-to-back depth. It gives you far more options for aquascaping, and much more room for items which are to be placed on the substrate.
If you really want the 6' length - go for the 180g (72" x 24" x 24").