I have an 8530i. I have had this phone for about a year, and haven't had many problems with it. Internet is difficult to use because the screen is so small, and text messages often come as fragmented, multiple messages that I have to decipher. My biggest problem is with Nextel. I have had them for 7 years and reception is terrible. I can't complain too much though because my service is free.
My suggestion to you is to buy a Defender Series OtterBox for whichever model you get. It has saved my phone on multiple occasions.