I'm working through my old atty bag that was full of attys that just weren't performing well. I have oodles of old ones to work through so I am gunna save a bunch on attys for a while.
As for what atty is ideal for the provari, ANY. Just use the ones you like best. I have run 510, 306, 901, and 801's off it and they all work splendidly. I have even run some LR attys that weren't performing well at 3.7 but came back when I dialed up to 4.
Since the connection is 510, you will need some adapters to run some of the other atty types. But it has handled everything I have thrown at it without issue