Or??? That is some kind of blasphemy...
I have both. A 7904A and a 7104, to be precise. I wouldn't mind having a 7904 because it has some features that are handy that were deleted from the 7904A, like a current loop calibrator for current probes. However, the 7904A is easier to work on because it uses the split case design. My 7904A is my workhorse lab scope...I keep it on a scope-mobile. I also have a decent selection of plugins for it, which store on the cart nicely.
As to the 7104, as long as the mcp isn't pre-destroyed for you, it should last a long time in hobbyist use. Just be careful to not crank the brightness way up when it isn't needed (the protection circuit helps, but it won't fully protect you from stupidity) and you'll be fine. Definitely want 2x 7A29 vertical amps and 7B15+7B10 timebases for full bandwidth operation. I'd like to find some 7A29s for mine with the variable delay line option, but those are scarce it seems. I use the 7104 when I need the speed that I can't get with the 7A19 vertical in the 7904A. I also have a pair of P6201 FET probes that I use with the 7104; they complement the scope perfectly (and there's probe power on the rear panel of both scopes, intended for these probes). Very handy for looking at higher speed digital signals in projects. Be warned that there are a few 7k plugins that
must never be used with a 7104 because they will cause damage to the mcp. TekWiki does a decent job of calling them out, iirc.