I've used them all, go for SPD-SL.
Keos hang weirdly and inconsistently making clipping in sometimes awkward, I've also snapped a carbon bladed one by standing on the underside of it. Speedplays are awful for any kind of walking in and the cleats cost £60, also the tension is not adjustable only the angle/float.
Time RXS snap, both cleats and pedals, I've done this to two pairs. Also the bearings are shit and develop play really quick.
SPD-SLs aren't perfect as if you increase the tension to unclip then it also increases the tension to clip in, but the cleats are the cheapest, longest lasting, the pedals hang nicely so they're easy to clip in to, the bearings don't seem to develop much play over time and even if they did the pedals themselves are the cheapest. As for tension for back pedalling, I use them for fixed crits so yanking against them on a big gear and they're solid.