We definitely find these to be the most likely to reward points. They are also very easy to complete. However, there are a few drawbacks with them that you should pay attention to.
The most obvious is that some cost money. They may also not be something that you as gamers, would be interested in buying in the first place. Also you're probably on the site to get stuff for free, so why spend money right? However if it’s something you’re interested in purchasing anyway then at least this way you’ll get a points reward too.
The second is that you have to be aware who you're giving your personal information to. Research any place you're going to give your information too. If you see lots of negative reviews or comments mentioning it's a scam, avoid it.
So what does that leave? Look for trial Quests from large businesses. Netflix, Amazon, Huluu, Blockbuster, Fedex, UPS, Redbox Instant. These are all trusted companies. Make sure you are really on one of their sites before submitting anything; don't fall for third party sites. Read the terms of the trial, how long you have to cancel it, what you get, how long you have to keep it active for to be eligible for the points reward. These companies are willing to pay for these referrals because people sign up for the rewards and fail to cancel them in the allotted time. Don't be one of these people. Also note that this requires a valid credit card to complete these Quests, something not everyone has. However if done correctly these Quests can easily offer 10k-40k points for free, just for remembering to cancel a subscription!