I don't know why but I prefer the vest harness' like seen on the flying coasters as I feel both free, but comfortable, but also snugly in the seat - nothing digging in and nothing to smash my head against - however some people dislike these?
I do love a good B&M OTSR with the clicks, as I have always been a funny weight where the harness is a touch loose (if I go 1 more click, i'll struggle to breathe, but it feels it could be a few mm tighter) - adds a bit to the scare factor especially on things like oblivion!
However, as I said i do prefer the harness' on the flying/winged coasters as they're more of a snug fit, and can be stopped at literally every point (Technical terms aren't great here as my knowledge is limited - however the harness' on nemesis for example goes down in clicks, and you can either have it at 1 point or another, no in-between - whereas the flying/winged coasters, the harness' can be stopped at any point allowing you to have the perfect fit) Which is what I prefer =D> a mix between tightness and comfortable