If I could choose 1 power it would be to make everyone content with their lot.
Remember Caz. Never argue with an idiot. They will drag you down to their level and beat you with experience.
But without having to drink (Louiellen's) blood like a vampire does, without ageing and withering away and looking like a prune, without getting ill ever and with regenerative powers in case I have a nasty accident.
So, not a big ask then.
Of course, it'd be tough as hell watching your family and friends all die off but I'd be sure never to get involved with anyone special in the future so I didn't have to re-live such a thing over and over.
It's purely because I've always wanted to see us make it to the stars and to go to alien planets myself. Maybe even meet other life forms. That whole thing fascinates me - but I never will because ... I'll be dead by the time it happens.