One: The more members a gay dating site has the more likely you are to find lots of guys in your area to choose from. Of course more guys in an area means more competition so in some ways it's all relative but you can't go wrong with volume. If 100 gay guys in your city are on the gay dating site it's going to be harder to get laid than if there were 10,000 gay guys in your city on the site. That's why it's always worth joining for free (most sites in the genre let you do that) and doing a quick search to see the number of results available to you.
Two: You want a simple and elegant design for your gay dating website. If there are too many bells and whistles it can be a hassle to use the site and over time that will wear down your desire to get on and send out messages. If there are too many clicks involved or it's simply too complicated your energy for the whole process will be sapped. Plus, the better looking the site is the more likely guys are to sign up, which gives you more gay guys to choose from.
Three: You want a site that's as much about helping you get laid and get dates as it is about making money. I mention this because there are far too many gay dating sites (and dating sites in general, straight or gay) that bombard you with advertisements so they can squeeze a few extra bucks out of you. If you actually want to contact gay guys on almost any of these sites you'll have to become a member so they're already getting money out of you and then they're trying for more with ads, premium features, etc. It can be incredibly annoying if you're just trying to meet a man.
Four: You want a gay dating site with variety. Gay guys are into all different kinds of men and a good gay site will offer you that. There are a handful of quality sites that get really specific but in general if you want to explore all that is wonderful about gay dating you should go for a wide-reaching site that can help you explore your desires and discover needs you never knew you had. On the other hand, if you know exactly what you want you can try a gay dating site that caters to your specific needs.
Five: Look for a site that offers its services for a reasonable fee. Gay dating sites are looking to make money off of gay guys that are looking for love and there's nothing wrong with that. The only problem is that some get a little grabby for your cash, charging way too much for a membership. Those sites should be avoided. You'll know them when you see them. You'll be eager to meet gay guys and then you'll see how much they want a month and that desire will evaporate. That's how you know you've been put off by the price.