Pollywog

Heck, it doesn't even have to be a trade-off of one or the other. You can have the leg straps tied together with the usual bungee cord attached to a tab on each leg strap, so that you eliminate the slipping leg strap problem, without any down-side of having loose stuff flopping around behind you in the vicinity of your pilot chute bridle. And since that can be done, then you don't need to accept even that small risk of using a pull-up cord to tie the leg straps together. Just have a rigger set it up properly for you, without jerry-rigging it. My 2¢.