I have my eye on 2 omegas
one is omega speedmaster mark 3 automatic
or should I buy the omega speedmaster pro.?
not new both are from 1970s

Yes Peter, you should buy both, but you should send the Speedy Pro my way if it's in good shape!

which has the better band?

mark3 and I think they did not make as many as the speed pro. so might be more on resale if I decide to sale in future but I hoping to keep it for now.

I don't know. Speedy pros just keep going up. Just a few years ago you could get a decent one for ~$800, now they're going for >$2k. It's a great design, and true classic. The Mark 3 is a bit funky and dated looking to my eyes.