90g or 120g debate

[Delphinus]

It's a no-brainer, the 24" of depth (the front to back dimension) leaves you WAY more aquascaping options. Always go with depth.

If it's a DIY built stand, it would not be too difficult to "dress" it up a little, if you're a little bit handy. For example, since the structure is already sound, you don't have to worry about the exterior providing any additional support. Thus you could go with a thin layer of plywood, stained and varnished, and maybe some cabinet doors.

Or heck, do as suggested and build an inwall tank. Makes for a super quiet tank viewing experience.