The A8 sounds like the better system for you. The strength of AM3/AM3+ systems is the ability to run 6-core and very shortly 8-core CPUs plus have a lot of PCI Express bandwidth for graphics cards and other expansion cards. Llano CPUs on FM1 have much better integrated graphics and a lower cost overall than an AM3/AM3+ Phenom II system at the expense of less PCI Express bandwidth and no ability to upgrade past quad-core CPUs.
Your usage patterns are pretty light and you would be much better suited by the A8 due to its better integrated graphics. You could replicate the A8's graphics performance with the Phenom II system with an add-in card, but it would cost more, run hotter, and use more power.