50k on United will get you Premier Executive which would make you Star Gold. That perk (not sure if it's relevant to you) will give you lounge access at any Star Alliance lounge on your international itineraries. I'm not sure if Delta offers anything comparable to that. As far as upgrades to Africa, 1P is not enough to get you any System Wide Upgrades (SWU) so I believe you'd only be able to upgrade using miles but I believe that is not any worse than what Delta offers. As for award flights domestically and internationally, United is the obviously superior program here as Delta is notorious for making it hard to find low tier award tickets as you'll see all over their forum. Hope this helps!