i'm not sure how much overclocking i'll be doing, but i would like a heatsink and fan that's pretty good, and 100% fits the other parts, no guess work required :]
the stock heatsink is actually pretty good, if you dont intend to OC to more than about 3.6ish you should be fine with the stock one. If you want to OC higher the mugen II will be good.
You will need to remove the original AMD h/s bracket and install this one while the mobo is outside of the case, and you will need a screwdriver, but all in all, it shouldn't be too bad.