The 1080Ti and 2080 are basically the same speed in regular rasterization, but the 1080Ti are way cheaper, so for traditional rendering it's a no brainer, the 1080Ti wins.
Only get the 2080 if you care about the new RT features, just beware that no games support them yet, and not many will in the early years. And most likely the games that do make use of them are going to be restricted to 1080p because performance above that will be terrible.
DLSS early doors looks like it's really no better than current post processing AA techniques, too much blur and loss of IQ, it runs better than MSAA but looks worse, FXAA is already so cheap that the performance impact is basically negligible so if you're happy to eliminate jaggies with blur then DLSS really doesn't bring anything to the table, it was just an attempt to keep the new RT cores busy.