If I were to get a 120g tank I'd want the 48x24x24 size. The 24" depth is sooo nice to scape, can't be found in smaller tank sizes, and is the best benefit of a large tank.
For filtration one or two 2217's combined with a big Aquaclear HOB should work well.
The more I look, like this size tank and it might work for the area I have to work with. Now to find one. ha ha