Why do a poll when at the end of the day it's your kit and you should run what you prefer?
I bet I could probably ask this question to a bunch of people, and get several different answers. I could probably find at least one person who would answer with each different colour. Black, Coyote Tan, Coyote Brown, Ranger Green, Olive Drab, Multicam. I'm sure there is at least one person out there that prefers each of those plate carriers to be worn over top of MARPAT.
Now, that doesn't mean that each of those choices is a good choice. And if you did even a couple minutes of searching this board you would have found that out. Because this question gets asked all the time, and the answer is the same every time. Coyote tan/brown works the best over MARPAT. It blends well with the pattern, and it blends well with a wooded AO. Going with a flat colour also gives you the ability to run the same plate carrier over several different uniforms of various patterns.
If this was just a general question asking what everyone's favourite pattern for gear is, then just go check out the Loadout picture thread and your answer will be whatever that person is wearing. Or if you are asking what the best colour gear to wear over MARPAT is, well the most effective will be Coyote Brown. But, that doesn't necessarily mean you have to wear it, you could just pick what you think looks the best, build your kit, and stop caring about what other people think about your kit (unless of course you make some really bad choices, ie black gear, and someone tries to offer constructive criticism to you, then that's a completely different story).