I am running Redline and have room for either but not both. Given the current meta which is the stronger choice. Which do you prefer?

Depends on your meta, but Generally Protons are better if you have the points as one focus result to Crit is just better if you have the points

That is what I was thinking but since U Boats run both i thought I might be missing something.

less a question of which is better and more of what else you could do with the 1 point difference

and that depends a lot on the rest of the squad

protons are far more reliable; plasmas cut through green dice very well which is very useful against inquisitors and aggressors and are cheaper