One thing to keep in mind, though, is that:

a) Stillwater is established and maintains an inventory, while the other is new but offers a wider variety of tartans.
b) Stillwater's site also only allows you to order items currently in stock. I, for one, have been watching their site for the past month waiting for them to get a SWK standard Black Stewart in a 36" waist... it hasn't been available, so I couldn't order. With FC, you could order, but would be waiting until it came in.

Really, the 2 more or less get their stuff from the same places. One, you can't order or pay until its in stock. The other, you CAN order and pay, but may have to wait.

The only thing it really comes down to is communication, and some people's instant-gratification expectations.