Dual Enrollment

I have been hearing a lot about how it’s bad for admissions chances to take courses at a local city college instead of taking equal courses at the attended high school of a student, it supposedly has something to do with how colleges want to see students competing with their peers in the grade that their in. I would like to take lots of courses at my city college, since they are taught at a more rapid pace, have convenient scheduling, include less pointless units/projects, and are generally more intriguing. So which would be best from an admissions standpoint and why: taking city college courses, or taking courses of equal level at high school?