In general, I would say you should go for more separation. But, that's a general case, and there's always exceptions. If you watch Stan Wawrinka, he often hits later and closer to the body (less separation) than most one-handers, and he hits the ball incredibly well. It requires better timing as it sometimes forces him to rotate through his shots as opposed to letting his arm go through the hitting zone and then opening up his body on the follow through, so I wouldn't recommend it to most players, but for him it works.
So overall, I'd say for most people it's better not to get too close to the ball, so that's what I'd recommend, but clearly it's possible to hit a great ball without a lot of separation, so it's up to you.