Can we just agree that
PhotographyIsConfusing is just posing as a noob to ignite a flame war?

OK, just kidding.
Really, no DSLR these days is better or worse than another. Image quality is about the same regardless of brand. You should be paying more attention to good lenses as they determine more about image quality than camera bodies.
Go to a store, try out a bunch of DSLRs. Get what feels best in your hands and what you feel will best suit your needs as a system.
Nikon is probably the best when it comes to backwards compatibility with lenses. They've used the same mount (albeit, with some modifications) since 1959. Certain
very old lenses will require some cheap modifications to work on some new bodies. You can use DX (crop sensor) lenses on film bodies, although you'll get black corners at most focal lengths. You can use DX lenses on FX (full frame digital) bodies, and the FX bodies can automatically recognize DX lenses and crop the area of the sensor that gets used to avoid black corners. You can use FX lenses on DX bodies with no problems at all.
Canon bodies and lenses have full compatibility since the mid-1980's. Canon changed mounts at that point when they moved to auto-focus systems, so, old Canon manual lenses are completely incompatible with newer Canon bodies. You cannot use EF-S (crop sensor) lenses on EF (full frame sensor) bodies, not that you'd really want to anyway. You can use EF lenses on EF-S bodies.
I know a lot less about Sony. They bought out Minolta and now uses their mount, so I think there is a decent back-catalogue of Minolta lenses if you buy a Sony.
I don't really know anything about Pentax.
Olympus is really the only brand I think some of us will advise keeping away from. They use a smaller sensor (2x crop compared to Nikon's 1.5x and Canon's 1.6x), which does affect image quality in some respects.