Having spent some time recently scoping out HTPC ideas, there are more parameters to consider, I think: is there a size limit/preference? Preference for style of case? Any gaming to be done on it (light or heavier)? Budget?
For me, I wanted an HTPC that could do light gaming for the kids as well (Minecraft, Lego games, platformers, some kid-friendly racing games, etc.), and the size limit was set by our desired TV cabinet (so anything up to 38cm deep and less than 20cm high).
For this I've started pulling together parts for an AMD FM2+ rig using the new Kaveri APUs with some fast RAM and in a Cooltek G3 case (or possibly Silverston GD09).
If you want a lot of storage you'll need a different case, of course, as the G3 only has space for 3 3.5" drives (though that could easily equal 12TB...). Does it matter how big the computer is? Did you have a case in mind?