I have a Gigabyte 4gb full tower rig with an ATI 4650 video card and four hard drives for 3tb of total storage running the Phenom 955 and was very happy with it. I don't really play any games as I built this rig mainly for video editing using Pinnacle Studio 14.
I was very happy with it although I had a lot of problems with OCZ DDR3 1600mhz and RAM. It would only work at 1066 mhz and took me a while to figure it out. It was crazy because I had issues with lock-ups and restarts before I figured out that this RAM would only work at 1066 with my setup.
I switched to Corsair, which initially worked at 1600 mhz then when I switched pairs because of a much better price, it would only work at 1333 mhz.
I bought the Phenom x6 1055 from Tiger Direct at a fantastic price and popped it in. I updated the bios before making the upgrade. I changed processors and had to drop the RAM speed to 1066 again. It had been very stable and there is definitely a noticeable speed increase over the 955.
Basically, if you have the 955 now, don't upgrade. If you have a choice of the two, get the 1055. You will be happy.
BTW, Intel is faster but the price is not worth it unless you get it for free.