If you look at the numbers, acceptance rates of Early Decision are definitely higher.
For instance, for the Fall 2016 entering class, Swarthmore admitted 214 out of 634 ED applicants (33.75%), UPenn admitted 1336 out of 5762 ED applicants (23.19%), Cornell admitted 1340 out of 4882 ED applicants (27.45%), Duke admitted 816 out of 3455 ED applicants (23.62%), etc.
However, lower acceptance rates in the Regular Decision may not necessarily mean your chances will be slimmer.
Acceptance rates of Early Decision are higher because the number of applicants is lesser. The applications received in ED consist of those students who are definite that they want to come to that specific college. Therefore, most of their applications are very polished. Almost all students competing in the Early decision fulfill every requirement of the college and are highly qualified for the institution, meaning the competition is extra-rigorous.
The cohort in the Regular Decision consists of all kinds of students. Many high school students apply to 10s of colleges just for the sake of applying. Acceptance rates seem lower because of the astronomical amount of applications colleges and universities receive.
If your academic statistics are logical, and you think you’re best suited, for a specific college, apply for ED!