As far as how interesting the areas are, ebonheart ftw. So much nostalgia there for the players who played all the previous games (especially skyrim and morrowind). Aldmeri dominion is next, it's just quite awesome and magical. The covenant areas aren't quite as interesting terrain-wise. As for what I play, ebonheart is the way to go. Most diverse race-wise (1 human race, one elven, and one beast. DC is 2 humans 1 elf and AD is 2 elves and one beast). The lands of morriwins, blackmarsh and skyrim are very colorful and nostalgic. The lore in the areas can often be connected to the other games (the tribunal for instance is quite interesting). And of course, nords, argonians and dark elves contrast each other so well that's they each make the game very interesting in their own right. Tldr, ebonheart pact wins.