I went from one of those slip on silicone sleeves to the ballistic. The slip on sleeve wasn't secure and you could feel it slip around the edges, but it was better than nothing.
Then, I recently picked up one of these:
I like it even better than the Ballistic...pictured here:
I never liked the large rounded corners on the Ballistic, although I can see how they add a ton of drop protection.
The newer hybrid case has the hard plastic part UNDER the silicone cover. It fits snug to the phone, leaving no gaps. It does fit better and smoother than the Ballistic. The only thing I could nit-pick is the flap that covers the charge/USB port and earphone jack. It close snugly, but when opened, it seems to be stretching and pulling at the silicone. It needed a better "hinge".
The hybrid cover isn't as heavy nor as bulky as the Ballistic. But it feels like it would protect as well in a drop. I like how the plastic under layer fits square to the screen. I could always detect a little "curve" to the lines of the Ballistic cover, and that bothered me a little! But both will do a great job of protecting the phone from rough handling or drops. The Ballistic feels a little more "tacky" than the "Hybrid".