Mostly alternate between two, depending on load.

A Patagonia frameless (model disremembered) for lighter loads. It fits perfectly and has hip belt wings for load and motion control, ample pockets and is reasonably watertight.

A Gregory Z20 for heavier loads. With a perimeter tubing frame and trampoline mesh backpanel, it rides well even with snowshoes attached and isn't sweaty. Fit, as above, is perfect for me.

Cheers,