I really like Mypoints. I used to do Milesource but I don't bother anymore, Mypoints blows them away IMHO. I joined about 2 1/2 months ago, and have already earned two $10 GCs and a $25 GC. I do more than read the emails and take surveys, though. It depends on how fast you want to accumulate points and what you're willing to do for them!
Most of my points were earned through the "Try It" offers. You sign up for a service or membership for a trial period, and you get points (maybe 200, 400 or even 1500). Plus most of these offer additional incentives. For example, I got 2 $10 Home Depot GCs plus 200 points for signing up for Complete Home, another 200 points plus a $10 Red Lobster GC for Great Fun, a $10 rebate on gas plus 400 points for Reservation Rewards (although I'm still waiting for those points

), and 1500 points for trying a video for 10 days. The trick is, you have to be very careful to read the fine print. Make sure you know when you need to cancel by, and make sure you do it before you get charged a whole year's membership. If it is a trial such as the video 10 day thing, make sure you send it back within that time frame.
Then I ordered the video Ice Age for 1000 points, and have placed two orders from Tupperware for 800 points each. A little shopping at the
Disney Store and Book Closeouts for 2 points per $ spent. Just a tip, make sure you save all of your confirmations in an email folder, don't just print them out. And also keep track of how many points you were promised and when. If there is a problem getting your points, Mypoints will ask you to email them proof.
I think it's a great rewards program. Good luck!