I use e-miles and e-rewards when I'm stuck on hold on the telephone, and I find both pretty painless.
I used to do Opinion Miles, but I'm not going to anymore because of their frequent use of bait and switch. At least 5 of the last 10 supposed surveys have started as a survey only to morph into an ad trying to get one to pay for more survey opportunities. If you don't sign up, you get no credit for the questions you have answered. When you write to Customer Service, they just say that they have to control over what their clients do--tough luck! What a sleazy company for United Airlines to be aligned with.