Whichever one you choose, get Iridient Developer for sheer quality.
What usage - landscape, humans , colour, b&w ?
Do you have glass that you can use via an adapter on the fuji?
The Sigma is a brick, not versatile, plastic but under limited situations can produce exceptional files. The Fuji - I've got both (actually all three, DP3 too) - think Leica gestalt but with autofocus, if you want it, plus live view and focus peaking. I still use the X-E1 and, unless you need wi-fi, gives away little to it's newer sibling. Don't underestimate the versatility of using existing lenses on the aps-c sensor.
IMO, if you're doing landscape and still-life probably the Sigma - for the rest Fuji.