That's a tough call .. Both are really nice mango's. The Pickering will be smaller and slower growing, yet have larger fruit. Both fruit are very good, and quite different. It's a matter of personal opinion as to which one is better in regards to taste.
I have not had any Pickering yet this season, so it is difficult for me to choose one over the other in regards to flavor ...
If you were in Florida, I would lean towards Pickering. But in California, it might be tough for the tree to put on size..