Currently, I use Ipsos iSay, Opinion Outpost, ProductTube, and Swagbucks. So, I'll read through their reviews of each.
Ipsos:
They rated it fairly highly and I have to disagree. For one, their site is atrocious. Have of the time you go to do a survey you get a message about coming back in 10 minutes because the site and/or survey is messing up or you just get a "service unavailable" message. Because of this, I only go to the surveys they email me and this cuts it down a little, but it stills happens and it is still annoying. Second, they take forever to payout for Paypal. They say it can take up to 3 weeks. Typically, I get my payment in about two weeks. Third, for the focus group and special offer surveys the payouts take forever to come or they never do. I had to email them about three surveys I did that never paid me (I waited until after the typical 6 week cutoff mark to email). Two of the issues were resolved after a ton of back and forth. The last one was supposed to have paid out in 7-10 days and it has now been 10 weeks and I still haven't gotten the $45 owed to me. That's after Ipsos confirmed with the project manager that I was supposed to get it. They have been telling me for three weeks that they are adding the points to my account. With all that being said, I make about $15 a month pretty passively. I try to take a survey when it gets emailed to me and when I complete it that's fine and if I got an error message I get over it because I'm so used to it. Plus, I have gotten a couple good product testings from them. Also, you get 5 points, 5 cents, if you are disqualified from a survey. While that doesn't sound like much it is better than nothing. As for redemption levels, you have to have $15 for PayPal and I believe $10 for Amazon.
Opinion Outpost:
Also rated highly and I agree. By far my favorite one to use. The payout is super fast, most of the almost instant. I think the longest I have waited was two hours and that was on a weekend. I get a lot of product testing through them and several great focus groups. Some downfalls, you have to wait until you have $5 to get Amazon credits or $10 for PayPal, but that's better than other sites. Their customer service is lacking. If you ever get wrongly disqualified from a survey (ie you actually completed it, but got directed to the wrong screen) they never give you the points. Also, it takes a while to start getting in a lot of surveys, but once you do it is easy to rack up the points.
ProductTube:
This one isn't on the site. I just found out about this one this week on here actually. On this site you take videos and submit them to the company for research. So, I signed up and did the first snack survey video. I shot and sent in the video (2 minutes long) yesterday around 2pm and I got my $5 Amazon credit by 6pm. I've also been emailed the first survey offer from them which was for $15, but I was disqualified. Overall, I think this one will be nice. I'm glad I signed up even if I don't get any other offers, because I've already made a quick $5.
Swagbucks:
Highest rated of the 3 on the site that I use, which isn't surprising because it is the favorite of many and I have to agree. This month I cashed out $100 from them. I make most of my points by doing surveys and some of the quick and free special offers. However, they are bad about surveys not crediting or wrongly disqualifying you and a lot of the special offers won't credit you either. You can submit tickets for these, which I did for the bigger point ones, but they get to the point where they won't credit you anymore. There used to be a long wait for payouts, but now I think they all come in about 1-2 days. They also have $3 Amazon cards which is nice if you want to redeem for lower values. Or you can wait and save 2200 points and get one $25 card once a month, after that the cards are 2500 again. They also have other denominations and a ton of options for redemptions. As for the surveys, Swagbucks often rewards you with less points than if you did the same survey on Opinion Outpost. For example, I have gotten similar magazine surveys on Opinion Outpost and Swagbucks and OO gave me $1 while SB gave me $.60. This is because Swagbucks is a hosting site or gateway for other survey companies. Because of this, surveys also tend to get filled up quickly. Lots of people make their money running the video apps, but I've never done those. There is also a reddit board dedicated to it if you want to look into this one further.