Intel HD Graphics is still poorly supported by XBMC 12 Frodo for interlaced contents (the playback freezes if Deinterlace video: "DXVA Best" is selected, so you will be limited to "Bob" or some kind of crappy software deinterlacing ). AMD is the way to go for XBMC. If you play only films, either platform is good, of course. (Film is also bad with Intel + XBMC 11 Eden, 12 Frodo is better in this regard.)
Ok, does not sound good with the missing support from XBMC! What would a good alternative from AMD be ?
A6-5400K, $70, is enough for almost every video playback task including BR 3D. Its graphics is overall better than Intel HD Graphics 4000. The processor (dual-core) is a bit weak for, e.g. 2D-3D conversion and real-time transcoding for another device such as iDevice. A8-5500 quad-core is a good choice for these purposes, in particular inside a mini-ITX case. The height of the stock cooler is 40mm, btw. Either ASRock or MSI mb should be good and either DDR3-1600 or 1866 is good, no big performance difference.