In order for the mutant hood to not flush, the suit has to fit pretty tight, otherwise you're going to have a gap between the hood and your body. I'm guessing if the mutant isn't working for you, maybe you should look at a suit with an integrated hood and draw-string to keep things as tight against your body as possible, like an Xcel or RipCurl.
I have a mutant as well, but no problems of flushing at all.. the suit fits me pretty well though. Its safe to say that any suit that is too big on a person will probably allow water into it...I think it may not be the brand itself but the fact it doesn't fit right on you.
The detachable hood is convenient to use when in the warmer part of fall and spring when you dont need the hood attached...but it's not a deal breaker.. stay with the chest zip however!
Never a separate hood, my dad has one and whenever he looks up while paddling, the neck comes up out of the suit. Unless you get the full vest, but like everyone else said, just stick with the attached hood.