I've taken the SAT twice, and my superscore is a 2190. The issue I have is that my critical reading score is not up to the same level as my other scores (660 vs. 750 on Math and 780 on Writing). I decided to take an ACT practice test as an experiment and got a 33 without any prep. Now I'm in a dilemma - do I take the SAT again and try and improve my reading score, or do I give the ACT a shot instead?
Take a couple more ACT practice tests and see if you can improve your ACT score even more. Right now your scores are about even with each other, but I agree that your SAT Reading score is somewhat of a concern if you're applying to the most selective colleges (which I assume is the case if you're still looking for a higher score).
If you can get your ACT score in the 35-36 range after a little more prep, I would go ahead and take it instead of retaking the SAT. If you can get a 33 on the ACT without prep and you've struggled with raising your SAT score from where it is now, it stands to reason that the ACT is a better fit for your skills.