Assassin's Words of Wisdom:
Pentium Processors are more powerful than their AMD counterparts, however AMD's do boast a little better graphics performance. Both do HTPC's very well.
If you are unsure which one to use, Intel processors are a safe bet and what I would recommend. Intels are more power but AMD's have better graphics (for gaming purposes not media playback) however AMD's typically run hotter.
For standard HTPC purposes, an i3 processor is what I recommend and all the processing power that you will need and has great graphics capabilties as well. Our i3 systems can handle (5) 1080p video streams at one time without using more than 20% of the processing power. The 2.6GHZ Pentium is a great budget processor that can handle a lot for its inexpensive price tag and is perfect for bare bones and extender systems.
So why upgrade to an i5?:
1) Possibility of very large media/music libraries (500+ movies).
2) Some processes (ripping, burning, etc.) are faster with an i5.
3) Better graphics capabilities for mid-level gaming (marginal)
4) Possibility of high end computer gaming and graphics card addition in the future.
5) Sense of security (this is honestly why most people upgrade). Just knowing they have a little overkill on the processor side of things lets their minds rest!
So why upgrade to an i7??
1) Possibility of computer gaming in the future.
2) Even faster processes than the i5.
3) Sense security knowing your HTPC processing power is many many times more than what is needed.
4) You hate money.
NOTE: The new Haswell CPU's REQUIRE either an H87 or Z87 Motherboard.