Your question is specifically, which is more intense. Most people are just giving answers on which game they prefer, or just thoughts on both games. That is absolutely fine too. I've enjoyed reading the replies here, very interesting!!!
I would say omaha is typically more intense based on the fact there is just more action, and margins are slimmer, especially preflop. I could make the case that nothing is more intense than a final table of a large field hold em MTT though. I guess it can be situational in that respect.
If Mike McDermott was right, and holdem is the "cadillac of poker", then omaha is the ferrari.
As far as which game I prefer, I would say omaha, specifically omaha hi-lo (PLO8). Since you only asked which game is more intense, I will spare you the intricate details of my opinion on how the games compare and why I love omaha. I look forward to expressing that in a future thread, or here if anyone has any interest LOL.