I've got both HKs (P7, USPc) and a SIG (239 9mm), and they are both great manufacturers. I think it comes down to application.
In a combat situation, where I was going to beat the heck out of the gun, both would do quite well, but the finish on the HK is more durable than the SIG.
Trigger is FAR better on the SIG.
Both are extremely accurate.
HK (USP) allows C&L
HK P7 is probably the fastest gun on the planet to get into action during reloads
SIG ergonomics are excellent
Takedown and maintenance on both is a breeze.
Soooooo, take your pick of which one fits your hands better, and shoot with confidence.