Definitely the regular 616. The Ultimate Universe used to be much, much better than it has been the last half year. Bendis was doing much better, especially with Spidey dating Kitty Pryde, Fantastic Four was one of the best titles, even launching Marvel Zombies, and even Ultimate X-Men seemed to be a bit better. But, it's all gone waaay downhill since then. New creative team on Ultimate Fantastic Four just doesn't shine like the previous team (although, they didn't do too terrible of a job with their first Thanos storyline), Bendis royally screwed the pooch trying to take on Clone Saga and breaking up Spidey and Kitty before it even began, and X-Men is continuing it's streak of having crappy writing and crappy artists. The only highlight I'm currently seeing is Ultimate Power...but, I'm thinking it will take some time before we see that title reach completion. I'm sure the release dates for each issue will be continuely pushed back.
Of course, your biggest problem will be where to start in the 616. At least by focusing on the Ultimate line, you only have to buy about 4 comics a month. The 616's main titles all are linking together lately, it seems. Currently, the X-titles are pretty much separated from all the Civil War stuff going on. But, Spidey, Avengers, Fantastic Four, Punisher War Journal, and a bunch of others are going to make you want to pick up more and more titles. (That's what screwed me when I got back into comics in the 90's. Infinity Gauntlet came out, and then I picked up all the titles it ran in....then, I got interested in those, and next thing you know, I'm getting all of Marvel's titles.)