If you're a (straight) guy without a partner, it would be better to have a female instructor, period. Dancing with men is just...different. Men are just bigger and feel different to dance with. If you're gay, then by all means, if that's what you're interested in, go ahead.
If you're a guy with a partner, then I would suggest a female instructor initially, while you're learning. When you get to be better, it won't really matter, although you should probably get coaching from both male and female coaches at some point.