One of the biggest problems with druids is actually that they add very little to your party other then Brez (Also I am fairly sure that Bear can cast Brez from bear form but correct me if I am wrong here) and the added benefit they do bring is best covered by a resto druid because of how strong their healing is. This is also the reason why Feral is considered a bad pick in solo play, even though DPS wise they are slightly above average, boomies just bring slightly more to the party so they generally get picked (and don't take up a melee slot).

So no, bears don't actually add very much to your comp unless you are running 5 druids like Elay said.

The change to the frenzied regen for bear is a slight nerf if your focus is DPS but I don't see that being an issue at the start anyway since you most likely won't get much DPS in on your healer. Problems with bears is that they nerfed rage generation so they get fewer Iron Fur's rolling in comparison to now (even if you exclude stat stacking). Even more so with the lower haste we have at the start of the expansion but I still think bear is middle of the pact (above warriors and for multiboxers, also above DH).

For trinity I think Paladin, DK and Monk will be top picks. Warriors are just in a very bad place, bears don't give you any benefit other then bRez (which you can get elsewhere) and DH have too big of a gap in their defensive skillset to make them stable tanks (which like I mentioned may not be a problem as a solo player, but a multiboxer faces different issues). The actual choice for tank will depend partially on your healer and of course whatever you like playing.

I was not aware they also nerfed the DH/Monk debuffs (I checked wowhead but they still showed 5%). This does make a minor change though because of how much dmg a paladin can currently push out, you have to offset the damage if you want to optimize (is 9% hunter dmg vs difference paladin > whatever you want to pick).

Ofcourse this will be very minor in throughput so pick whatever you enjoy most considering most people drive from their tank.