I've got a couple, and like everyone already said they've each got their pluses and minuses.
Hunters Safety Systems Pro
+'s: incredibly easy to get into, lots of pockets to store stuff, the Pro has mesh which breathes much better than the standard.
-'s: Heavy - even heavier when you fill up those pockets, the buckles for the legs are inside which can cause them to "clack" together if your knees are knocking (unsure how the new Pro model is, hopefully they put the buckles on the outside of the legs).
Muddy Harness (an exact, more expensive copy of the old Loggy Bayou Transformer harness)
+'s: super light, well though out addons for your binocs, fits under bulky clothes well
-'s: not as quick to get into as the HSS, doesn't have the pockets to stash minor items, kinda no frills for the money you're putting out.
AFA hooking up to the tree, the system that LoneWolf uses (very similar to the Summit SOP system with the rope and Prussik) is the best for me, and works great with either of the above harnesses I own - not counting the freebie's that come with the stands.