For point transfers, you can only transfer to the UR transfer partners, But each one of those transfer partners belong to an airline alliance, so you can book seats on the other airlines in the same alliance. It boils down to where is your departure city and which airline you like to fly with.

For HKG, the obvious choice is Cathay Pacific which belongs to OneWorld. That is tougher as UR cannot be tranferred to AA.

You can transfer to United and use it on United or other Star Alliance members. Before you do, you want to calculate whether it is better to do the transfers, or just cash out the UR points on the UR portal