my iphone hasn't come in yet, but i went out and bought a griffin grip vue. i can say i'm happy with that purchase. I've seen it in action and its a wonderful case. It makes your back look like a smokey grey so its quite diffrent, and it covers the sides hindering the signal issue.
Got a bumper when I bought the 4 but HATE that I cannot use my old charger cables, speakers, and other accessories with it. So I got FROGZ luxe blue case and LOVE it. Much better.
i bought a griffin reveal from best buy. looks like a bumper but has a clear backing. im happy with it. can use my ihome dock stick. headphones and 30 pin cables still connect without the case being an issue
At this time the best one is the one you can get quickly. I got one overnighted from Amazon and it arrived on Thurs (iPhone 4 on Wed). It works well but is a temporary one until better options are out there. And Amazon had sold out of it by Friday.
My case of choice has always been the incase slider. I use power support crystal films. If power support comes out with films for front and back, I'll stick with the black bumper I picked up and the films. If they just cover the front, I'll likely switch to an incase slider and get the front film.