I fully expect Ret Paladins to get retuned, because their current state in the beta sets them way, way above every other class in power level (Vegeta!?). It's not even that Arms Warrior kind of overpowered where Mortal Strike makes you cry delicious salty-sweet tears. It's that kind of overpowered where the guy wades into an entire Horde offensive, pops Divine Shield, and before a Priest can Mass Dispel it there's four dead Horde. And then the Paladin hits the priest with Crusader Strike, a melee swing, and abuses the Judgement of Justice bug to judge them for a 5,000 crit and force a Command proc for another 3,000 damage. All you can do is lay there repeating the word "what" out loud over and over.
The only other class rocking face as much as Ret Paladins is Mages. Let me tell ya, the new version of Living Bomb? That just ain't right.
Really, though, it seems like all of the Hybrids are really holding their own, with Ret Paladins at the front of the pack by far. All of this could turn on its head throughout the duration of beta with class changes and things of that sort, so who knows. Also, nobody is level 80 yet, and most people are wearing either now-outdated Outland epics (rating scaling has murdered my Sunwell gear, my 150 Spell Haste does almost nothing at all at 77) or Northrend greens.
Even the people in Season 3/Season 4 are getting destroyed, because level 70 gear just does not hold up against spells tuned for 80. The mix of S2 and S3 that I wore into the Battleground was little more than paper to Ret Paladins.
As far as which classes and specs are actually dominating beyond those two, it's really hard to tell. Warlocks are doing great, as usual. As far as Hybrids, I've seen a lot of Feral Druids and Elemental Shaman really holding their own, but the Mage/Retadin combo crushes their face all the same and makes it hard to gauge. I noticed Elemental Shaman playing guard-the-siege-tank quite a bit, using Thunderstorm to knock melee away from the tank. Feral Druids are doing the whole stunlock-a-clothie-from-100-to-0 thing, but it feels like they're fresh meat after that. This is only from watching others in the BG though, there's a chance those Druids were just terrible players. Which, perhaps, makes that full healthbar stunlock even scarier. Nobody really has resilience though, so maybe it doesn't mean much at all.
Feral Druids do seem to have a lot more survival and mobility abiliites than they used to via talents and spells, but I didn't really notice those come into play. It's very possible they weren't being used to the best of their ability, or lend themselves better to an arena setting where every move counts and combat is more of an organized chaos, rather than normal chaotic chaos.
I think PvP will be easier to test and gauge when the level cap is 80 and we can all get a bit of gear. Personally, I think Blizzard should hand out a set of basic PvP gear to everyone beta testing when they raise the level cap so we can really give it a whirl in a more balanced environment, but eh.
If you guys have any questions about the state of PvP in the Wrath beta, leave a comment and I'll see what I can find out for next time. I know I didn't touch on all of the class/spec combos, but the pool of beta testers (especially those PvPing) is small and it's hard to find them all. Still, if you want something specific, I'll give it a shot.