Is a 660 SLI better than a 770? Yes. Is it the best choice? Depends on who you talk to. If you can get them for the right price go for it. Otherwise you'd be better off with a single 770. Not all games can utilize SLI but most modern games can. Plus you have to make sure your PSU can handle two Video cards, and also that you can take the extra heat of an extra video card.
Thank you for the fast reply, the price really does speak to me for what I would be getting, and Newegg is offering 25 dollars off any purchase above 250 dollars if I remember correctly, Would a 700 watt PSU be enough?