Undoubtedly, this will deviate into a discussion on the premades, but such is life, as they tend to be the most "well known" and as such, in the eyes of many, the most promising.
My views:
NoName: Definitely - without any doubt - the tribe with the best *individual* players. That much cannot really be disputed. They have a pretty decent spread too. However, there are two problems (potentially) that one could foresee for this tribe - leadership and boredom. Most of us know a lot of the players in this tribe, and I think we can all agree (even they themselves would agree) that sticking around isn't exactly a habit for the vast majority of them. Obviously, should this happen, the tribe would be in trouble. Secondly, leadership. I don't think the "feelings" that Nauz and Kriegs have for each other are exactly the worlds best kept secret, so it should certainly be interesting to see whether they are able to work together effectively, or whether they will essentially implode. The only potential problem I see that could really stunt this tribe is their position being in the same area as CoDeD, another tribe I feel to be quite promising.
(It's also interesting to note that while I was writing this someone left NoName to join CoDeD in K44.)
CoDeD: Led by Ruffus, and that's all I really know about it. I felt they were somewhat promising but my views have dropped rather dramatically since Ruffus restarted - in another part of the world, as far away from NoName as he can possibly get. How am I expected to believe this tribe has any real chance of success if their own leader runs away from them? It'll be interesting to see, though, how things play out between CoDeD and NoName.
FOOD: Led by HumanInDisguise in an area that is (mainly) uncontested - as in, I can't see any tribes that would be anything much above decent there, yet. The tribe, though, is quite small and this could present a problem, especially early on, should diplomacy not be handled correctly. If this tribe survives until nobles and a bit past that, though, I would say they would have quite a good chance of success on this world.
DOGS: Know a few people in this tribe and they have a pretty decent spread. The competition in their area would most likely come from Fleeto (another premade). From what I know of this tribe and the few in it I do know, though, they could do quite well should they decide to stick it out on this world.
O.O: Know very little about this tribe apart from the fact that it's a remake of the same tribe on another UK world. They have a pretty decent spread though and if they play their cards right, could do quite well. Although, certainly, in my view, the weakest of the promising tribes in my list.