I think bars with more rise than most of the modern bends. as the older bikes foot peg to triple clamp
ratio is lower and makes standing up more of a stoop with most modern style bars
I use Tomaseli vintage , but they are quite soft and bend easily, I also like wider bars than most, seems to produce less arm fatigue than narrower bars but that may just be me
as a side issue some folk think fat bars (1 1/8) are a bit out of place on vintage bikes
but that's your call