What do you plan to do on the bike? Tires make a huge difference--i did my first metric century, 20 years ago, on a mountain bike with road tires, because that's what i had. i've also used my atlantis on dirt and gravel with 'cross tires, and it was surprisingly competent.
if you're happy with the performance of the tires you have, look for something that resembles them. if you do most of your mileage on pavement, you may be happier with less tread. why not go to a bike shop and look at what they have? by the time you factor in shipping, the price may come out close to the Internet, and you can ride the tires that day.
FWiW, I've probably had five or six different road tires on my 20-year-old Bridgestone mountain bike. They were all way better than knobbies, but none really stood out as better than the others.