No sponsor is going to come here and say "Our site is shitty, don't promote us" even if their site is actually shitty! They always claim they are the best.
No experienced submitter is going to give you the site they promote themselves and do well, they are not going to invite competition!
You need to choose 4 or 5 niches you like the best yourself, look around and see which sponsor offers those niches, visit the sites yourself to see what they look like, if you like the tour then give it a go. (you can also ask the sponsor to see how often they update the members' area, it does make a huge difference if you are going to use revshare program)
rotate niches and sponsors for 2 or 3 months and that should give you a good idea what is doing good and what is not. Try to choose from both PPS and Revshare
GreenGuy's Stats and
The Resource Page are good places to start with
Just my 2 cents!