I think the answer is "it depends".
It depends on snow conditions, and types of routes. If you are going up and down slopes, you will need the extra traction of the MSR.
Will you and your girlfriend be wearing packs?
I own a pair of MSR Denali Ascents. I have the tails for extra flotation but have only used them twice. Most of the time in the Sierra Nevada where we get rather wet snow, the conditions are consolidated enough that you do not need the extra flotation. I must ask where you are going where you expect the snow shoes to spend most of the time on your back?
I have seen many people have trouble with the fancy new snowboard like bindings of the MSR Lightenings. The older pull straps on the MSR Denalis and Classics seem more reliable and simpler.