I suppose mine would have to be a toss between Johto and Sinnoh. Johto has a good variety of places for you to go, such as Goldenrod and Olivine, and also holds a lot of history within its towns and cities. You'd also be able to visit the Kanto region, seeing as it is a neighbouring Region to Johto. It also has a decent amount of ocean, where Hoenn overdid it with the water. I'm a fan of water and with it, Water type Pokemon, but...
Anyway, as for Sinnoh, I'd say it has to be because of Snowpoint, mostly. As you can tell, I don't just like Water types, but also Ice types; they pretty much go together pretty well, if you ask me. On top of that; though it may lack short distance travel to other Regions, (thus far; it is unknown if Sinnoh is connected to anything, at its North) it does have a wide variety of places to go, such as Floaroma Town, Veilstone City and Canalave City, with its oceanic travel.
There's also the island, to the Northeast. It'd be an interesting adventure, travelling along the rough road of that little island.
As I said, its pretty much even, with Sinnoh and Johto, while Kanto is just behind, and Hoenn... well... lagging, we'll say.
for me, Orre is too boring; I'd rather be in a place where wild Pokemon roamed free, and I've actually never experienced Fiore. (guessing its from the Ranger game, and that's one I haven't played)
