It depends on the genre but generally speaking I tend to play as a male because I value immersion over visual appeal. On one hand, I would much rather stare at the finely sculpted ass of a female for 12 hours than the chiseled back side of a male. On the other hand, a hot, thin, scantily clad female kicking ass breaks any possibility of immersion. It's just not realistic. Generally, women are neither strong nor violent. The ones that are strong and/or violent are generally not hot. And by 'generally' I mean 'almost always but for very few exceptions.' People living in an alternate reality where there are no differences between men and women will call my worldview sexist. Fuck them.
I also avoid playing as women because, for some reason, "rail thin with enormous tits"--the preference of fourteen year old boys-- seems to be the trend for female player models in nearly all games. Fuck that, I'd rather have realistically proportioned females. If that were ever the case then perhaps immersion could be maintained while playing as a female character. For example, I had no problem playing as Raiden in Metal Gear Solid 2.
That said, as a completely strait male, I have no issue looking an attractive male physique for extended periods and appreciating it. Cratos comes to mind.