Well, I don't think colleges prefer one or the other, but I would say AP classes by a small margin. One, they give something that is well-known by the admissions officers and uniform - you used this curriculum, took this test, received this score, whereas dual-enrollment classes are a little bit more difficult to deal with credit transfers and what-not. Two, AP classes are either free or significantly cheaper than dual-enrollment classes.
I would only take a dual-enrollment class if they did not offer that course at your school or as an AP class (e.g., Calc III, so on). Otherwise, AP classes are easier to deal with in my opinion.