You want an AM3 for intergrated graphics over the i3/i5. Their intergraded graphics are more powerful than Intels. Also, the price for a build is much cheaper and provides higher performance compared to the i3/i5.
I would use Intel if I was going to build a HTPC today. Intel's latest on-board graphics are only SLIGHTLY slower than AMD. An i3 system uses less power than an equivalent AMD build. Another big benefit of an Intel HTPC is their TrueHD/DTS-HD MA bitstreaming support.
There are plenty of reviews of what you're looking for so you don't have to take my word for it.
... And ... Just for that, I am going to curse you with a "Best Answer" ... Not because you need it ... not because I think this thread is fully resolved ... BUT ... I curse you with this "reward" because my own Avitar has been staring at me from the "Latest Best Answer Sidebar", for nearly 3 hours, now, and it is really starting to creep me out ... and also because it was one of those "un-deserved" best answers.