I agree with a couple of the responses you have been given already. Its important that the cuckold experience be a "good experience" for the both of you. Obviously, you're doing this to add excitement and fun to your marriage, or you wouldn't really care for this forum's response. As the male spouse to our marriage, I could care less what color or how big the guy's dick is as long as my wife is getting a good experience from it, and the guy's respectful. We look at all our outside relationships ( M's, F's, and couples) based upon compatibility. So this means we're probably not going to be interested in instantaneous sex.
But trying to respond to the 2 choices you provide, I'd love seeing my wife taken by a very muscular, well hung, young stud ... and I'm almost 100% sure she'd want a more mature acting, physically fit, professional type guy.