Depends what you want your security soft to do.
OSA is better at blocking lots and lots of vulnerable processes, if you enable advanced settings. The only thing really missing in OSA, in that area, is rundll32 protection, and Andreas said he will probably add it.
ReHIPS free is a full-fledged anti-exe and it also isolates your Office/PDF apps, so you don't even need all that crazy paranoid vulnerable process protection.
I personally don't care about isolating Chrome and Firefox, they are secure enough anyways. There are no exploits in the wild that affect them, and there have not really been any for a few years. I have a beta license for ReHIPS, and sometimes I don't even bother to isolate Chrome, because I think it's overkill.