I have been using feedly for the past few months. So far, the experience has been pretty great. It doesn't really slow down for me, even on old computers running winxp. They are pretty quick to iron out any bugs. The UI is fairly simple and similar to Google Reader. These three factors were my test for finding the right alternative. I will be honest and say that feedly was the first one I tried out so I can not give you a comparison to others.
They are currently pulling the feeds from your google reader account, but will be transitioning seamlessly (or so they claim) to their Normandy project when Reader shuts down for good. If you do not want to take a risk with any bugs, issues, or delays that might occur, I suggest looking elsewhere.