I don’t think you’ll notice any difference tbh, Zee is perfectly good. Saint is definitely going to be stronger- it’s got an extra brace on the parallelogram- but XTR isn’t flimsy and I reckon is still stronger than the slightly monkey-metal Zee. And I dunno, the radr cage is very good but it doesn’t feel massively strong, the mech’ll always be as weak as the weakest part.
XTR makes most sense I think? Well, XT makes most sense, or sticking with the Zee 😉 But of your choice, I’d go with XTR for anything but a dh bike.
I don’t get the feeling you’re looking for cheaper options, but I’ve got most of a Saint sat in the garage doing nothing- it’s missing its jockey wheels and that wee bastardy bit in the clutch that always breaks, but you could swap the Zee bits into it, they’re interchangable. Just a thought.