I think I am going Dallas here. Other than Rose, Howard and Haslam(who at this point in his career shouldn't be getting big minutes) there's no really good players with any type of playoff experience on the OKC side. And I am not crazy about the quality of the players after Rose and Howard.
Dallas on the other hand is loaded with experience, playoff experience and much better quality talent depth. Nash on Rose is a mismatch but one I think Dallas can live with because they have the talent to shut the rest of the team down and just try to make Rose beat them. Also, Nash with Deng and Smith can push the pace and make Rose have to expend major energy getting back on defense.
I liked Houston's ability to match up against Dallas but I really don't think the Thunder have enough elsewhere other than Rose to take this series. And has been stated, as bad a defender as Big Al is, and he is not a good defender, he does well against guys much like him who are big and physical and spend almost all the time down low. Howard can't pull Big Al out and take advantage of Al's bad lateral movement and bad defensive footwork because he can't make shots outside of 5 feet. That mitigates Howard's overall effect. Howard will get his 20 and 14 but Jefferson will get his 18 and 12.
Overall I just can't see Rose and the collection of young inexperienced talent left over in OKC overcoming what Nash, Deng, Smith, Hansbrough, Gordon, Neal and Kaman bring to the table if the Howard/Jefferson matchup is fairly even.