You can convert SCI points to United miles, and then convert those to Hilton Points. I did that last year when Hilton was offering double points (four per mile).
Why Hilton? (Granted, they have more properrties and can freely exchange points/miles among partners.)
Personally I prefer Sheraton because:
1) Unlike Hilton, you can earn points at any rate.
2) Starwood owns Sheraton and the Luxury Collection, which includes St. Regis in NYC and Aspen (former Ritz Carlton's), the Phoenician in AZ, and others. A free night at those properties are 10K points, which is equivalent to 10K miles. However, consider a night at those properties can reach up to $300-$500, SCI is a wonderful bargain.