I would say that if you are ALWAYS going to wear the same boots when you're in conditions where you'll use your crampons, that I think I'd go for the step in bindings. One advantage of strap ons that I failed to mention is that they can be used with any boot, where step-in tend to be picky about footwear. I may be wrong, but I think Step-in are also designed for rigid soled boots, where strap-ons can be hinged and work with flex-sole boots.

MNS
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YMMV. Viewer discretion is advised.