If you boil down the question to the basics, just as it was phrased, "Which had the better cast?" then the nod from me goes to Enterprise. The cast choices, prior to the production of even the first episode, were very much in line with the potential that each of those characters possessed. Not so much with what the scripts eventually presented, but certainly there were times when the actors were so much better than the script that the show became painful to watch. The fact that ENT was painful to watch should not be blamed on the cast, especially not Scott Bakula (whose potential was never realized) or Connor Trinneer.
If it was not written in stone that T'Pol should be a sexpot wrapped in a potato sack with a Beatles mop-top, then I actually wouldn't have cast Jolene Blalock in that role. I would have preferred a more introspective, brooding, complex woman for that role, in which case I would have hired the fabulous Gina McKee:
http://www.bbc.co.uk/pressoffice/pressreleases/stories/2007/10_october/19/street_mckee.shtml
But Jolene did an impossible job: She made a character that ended up being written terribly, into someone at least sympathetic. And for that she deserves commendation.
On the one hand, the Trek 2009 actors each had impossible tasks: to succeed television's most iconic ensemble. But my feeling is that the casting agents rolled the dice with every one of these roles. With some, the dice came up box-cars. The one role I thought nobody could ever recreate, that of Dr. McCoy, was embraced and extended by Karl Urban brilliantly. And Zachary Quinto brought some new aspects to Spock that were quite enjoyable. Chris Pine...I'll give him another chance. I think I can accept him. I'm not expecting a Shatner impression, but I'm expecting a smoother James Kirk. Bruce Greenwood, superb. I liked him from the first moment. (I liked his Pike better than Pine's Kirk.)
The rest, I'm afraid, ended up for the most part being caricatures or hollow shells. I don't get a sense of Scotty on the screen, just someone (a very nice fellow, Simon Pegg) standing in his shoes. And with John Cho, as I feared, I think the casting agents were looking through pictures of Asian guys, Asian guys, more Asian guys, we need an Asian guy...hey, wait, wasn't this guy in that White Castle movie? Sulu was an intense, focused, ambitious, and sometimes debonair character; John Cho portrayed a fumbling idiot.
I did not appreciate the decision to have Uhura and Spock do a little romance thing simply because Uhura was the only female lead and she needed a love interest and only Spock seemed available. Time may have changed everything, but the two of them kissing in the transporter room was the most out-of-character moment of the entire film. Besides, the problem with only having one female lead could have been solved: Cast a strong actress as a completely re-thought Janice Rand, or as Christine Chapel (there's someone who might have tried smooching Spock for what it was worth). Then have Uhura's love interest be "Olsen," who gets fried by the Romulan oil rig. Not that I want to torture Uhura, but that would have brought depth to her character, and maybe made Kirk wise up and not be such a jack-ass (in this film).
And if you haven't seen the Rifftrax send-up of Star Trek '09:
http://www.rifftrax.com/rifftrax/star-trek
...then I won't spoil it for you by blurting out Mike Nelson's comment on Ben Cross as Surak. But I can't see it without ejecting whatever I'm drinking at the moment out my nose; it is the most accurate interpretation of that casting decision that could ever be uttered.
Anyway, there's my two cents, which became more like 14 after it was all said and done.
DF "Hey, You Know What They Say About Redshirts...It's Nyota, Isn't It?" Scott