Which do you prefer and why?

I prefer Reborn because it is much more comprehensive than Revisited. It has new quests, a lot more space for your goodies, and overall I really enjoy what Reborn adds to the spire.

Do take note that both of these mods replace the original DLCFrostcrag plugin, though, and that makes them inherently and unfixably incompatible with any mod that depends on the original DLC Wizard's Tower (the UOMP for Frostcrag, for example, cannot be used with them).