The A8 3870k is an APU the Phenom 965 is a CPU. Two different things in terms of performance. The APU has integrated graphics, the Phenom doesn't.
If you're looking for performance go with the Phenom 965, although if you want integrated graphics with an APU, I'll recommend you the A10-5800K a very powerful IGP (The A8-3800k is the previous generation of AMD APU's)
Don't buy the APU if you're planing to buy a dedicated graphics card.