Ebates has missed/not paid a purchase of mine here and there that I had to email to have them correct, but overall they're fine.
Do a search for Cashback Comparison or similar terms to see sites that list lots of cashback sites to see which ones pay the most for the store you plan on shopping at.
Be careful with some of them. Read the fine-print on how much it takes to cash out. At least a couple cashback sites require you have like $25 in cashback before being able to cash out any of it. That could take some people quite a while to get.
I probably use Giving Assistant the most. The % is usually good, and I don't recall it ever missing a purchase. It's set up to split part of the money with some charities, but you don't have to.