College rugby player here wondering which will yield the most benefits

Doesn't matter really, despite what people think the crossover from weightlifting to sports isn't such that sumo would be significantly better than conventional or vice versa.

I would go with sumo as conventional (in my experience) seems to be harder on your lower back / impairs mobility more

Mix it up. What you benefit from sumo you won't get from conventional vice versa

So is it really just a comfort thing? No benefit over the other as long as you're hitting the posterior chain?

yea, I wouldn't over-think it. you're getting the posterior chain work in. just focus on good diet and staying injury free

Sumo hits the hips/ glutes more. Less on the low back as compared to conventional.

do both

No neural adaptation will help rugby, not specific to the sport so your differences in motor neuron firing and MU recruitment (with respect to patterning) are small and irrelevant. Just go for metabolic adaptation

lolwat