I use to have a WRT-54G router using Tomato firmware. But when I upgraded my internet to 100mbit, the 100mbit connections on that router was actually bottle necking my speed. So I upgraded to a Nighthawk AC1900. But I was unhappy with its webUI speed, and lack of bandwidth monitoring tools.
So after seeing all the cool things pfSense could do I decided to use some of this years tax return to build one.
Breakdown of Parts: CPU: When I saw this CPU only used 25W I was surprised. And its more then fast enough to handle gigabit trafic they say, so I went with it. I also added a Passive CPU cooler since the stock cooler that comes with it has a tiny little fan and would probably be noisy.
Motherboard: There isn't a big selection for AM1 CPUs that I could find, and this one had good reviews and has everything I needed.
RAM: 8GB is overkill for a pfsense build. But I wanted to have multiple packages installed, and allowing squid to have 4-6gb of ram for fast transfers.
HDD: Wanted tons of space for Squid Cache files.
Case: Needed a small case, and I like that it has filters front intakes.
Network: I picked up the Intel EXPI9301CTBLK, to use as the WAN adapter, and bought the Intel EXPI9402PT off Ebay Used, for an Upstairs LAN, and Downstairs LAN ip segments.
Fans: NF-F12 for the front intake, and the NF-A9 for rear exhaust. Also because they are really quiet.
Power: Bought a PicoPSU 160-XT for fanless power, and low power usage, also had to buy a AC to DC power supply to power the PicoPSU. Also since I'm not using a normal case power supply, I bought a cover plate to cover up the huge hole on the case.