I would say posting and radio loyalty are the EASIEST.

Crowdflower has some easy ones sometimes but usually not worth my time.

The downloads are hit or miss and what to add lots of annoying toolbars.

Surveys can be frustrating when you are going along, been accepted and then middle of survey they pop you over to the "NOT qualified page"

WTF I was qualified enough to answer (X amount) of questions but suddenly I am not ?

Videos are easy.