With the two you picked, you can't go wrong with either. UPGP is a tiny bit trickier to apply with out streaks but don't let that stop you from getting it. Opti Seal is an awesome product as well. They last a hell of a long time. I have both and use them very often. On black I would use UPGP. I have a client that posts on here with a focus. I am amazed everytime I do his car and how the paint looks with the UPGP on it.
I *think* the OS last longer with fewer apps than the UPGP. I applied a single coat of OS to my girls car back in either January and the tops(hood, roof, trunk) still bead water when it rains, the sides don't but thats 9 months with one coat. I washed it two days ago and applied two coats to see what it will do.
Either one you go with you will NOT be dissapointed, they are phenomenal products.