1991 Marvel Series 2 and 3 Grading Preferences

[rogueriver]

Just bought a large collection of sportscards and have several sets and singles as well as sealed boxes of this stuff. I am thinking of selling them but I know absolutely nothing of the comic cards. Do collectors prefer PSA over SGC, the reason I ask is because I have thousands and the condition of these are some of the best I have seen as well as sealed boxes. The prices on these are all over the place to say the least which kind of scares me on grading at $15 a card Is there a good market for these graded. Any advise would help