I don't have either one, but to me, logic would dictate getting the SureFire. You'll have better interoperability in the field with other folks' replacement parts, if something happens to yours.
Then again, my 2 cents doesn't get me much these days
My shootin' buddy got the UTL that was made for the USP. Looks like it's made for the pistol if you know what I mean. Fits great, looks great and is bright as hell. He took it campin' a couple of times and it lit up the entire campground.
I do recall it being quit pricey however but it appeared to be of high quality. He likes his alot. Best, J. Parker
The UTL MKI only fits the USP, while the UTL MKII has slightly different rails to connect to both the USP and USP Compact. Externally, I don't see any differences. I have the MKI on my USP, and I really like it a lot.