IMHO the 5th ed published Tribunals are so different regarding political climate and Hermetic traditions it's a bit difficult to choose, because it depends on the kind of saga you want.
The differences regarding how a new covenant is established is especialy important for a Spring saga.
I'm very partial to the Rhine, IMHO it has everything: Deep, ancient forests with old magic, booming towns and cities, threats from borders, a rich Hermetic environment vital to interact with, political Gilds based on areas of interest - giving a third connection to other magi, after Houses and Covenants . New covenants need one supporting magus from each other covenant, so you'll end up owing favors. Although beware to not make the Gilds too conservative and the politics too stale!
I've played quite a bit here.
I also find Hibernia highly interesting and promising. We've played a little bit there and saw huge potential. The political climate is one of strife, and there is an overall theme of old vs new, Irish vs. English etc. Founding a new covenant is about proving oneself, fighting for it. Also, becoming a magus has elements of this with the macnimartha (sp?) where apprentices close to Gauntlet can run wild before swearing the Code. But all is not conflict, because "being a good neighbor" (at least to some) is what keeps enemies from ganging up on you.
Normandy I've never played in (well, not 5th ed Normandy). Vis is scarce and contested, ownership heavily regulated., covenants follow the classic liege-vassal relationships and raid one another. Lots of story potential here. To form a covenant you are likely beholden to one of the few powerful covenants, which can be both a source of stories as well as a pain because of lack of freedom. I can't say which weighs heavier as I haven't played in this Tribunal. The Hermetic Tourney sounds fun but I believe it will be a huge workload to manage.
I've played in Thebes for some years a while back. Interesting place with the democratic way of ruling Hermetic society, with "amateurs" drawn by lots for a limited time acting as leaders. This can be either good for stories or challenging to run, or both? The conflict among the mundanes between Romaic Greek vs. Latin invaders seems a good backdrop. A somewhat exotic locale yet still witin the old Roman Empire, cna be a good gateway to even more exotic places.
Transsylvania I've never played in, but the setting seems interesting yet you need to want to either play as or deal with House Tremere here.
Procencal I've never played in. The book seems fun because the Hermetic politics are so vanilla. Good stuff with House Flambeau and the Mitrans vs Mercurians. Yet you need to accept the Cathars and the crusade against them as an inevitable theme.