Gosh man it came out already The iPhone 4 came out on AT&T summer of 2010. Verizon's iPhone 4 has a few small changes from AT&T abd that will come out 2-10-11 If you meant the iPhone 5, that should come out sometime during the summer of 2011, no date has been set yet.
The iPhone 3G S, although there is evidence of a new iPhone comming soon that will come in 6 different colors of red,green,royal blue,violet(purple),light grey,and standard black. This is currently listed as iPhone 4G.
I prefer the iPhone 3GS. Primarily because it receives signal better and i find it's easier to hold but that's just me. Plus i like the variety of cases you can get for the 3GS which makes it much more personalised but im sure new cases for the iPhone 4 will come out soon enough!