Ah, debates about legs. I don't like this cuz it feels that people who support digitigrade legs act like a sect. No offence guys and gals but I've never heard any logical pros for digitigrade legs except squeaking that plantigrade alien looks like a man in the suite. But is it bad? No, it isn't. Looks and works great. Also, Predator looks like a man except its head and people adore it.
Just keep in mind: the most favorite by the fans alien movies have plantigrade aliens.
Also, digitigrade legs work perfectly for the alien-runner. But does it fit for a human-like xeno? I believe a person who said something like that, found the best solution: "Alien can change "bones" and joints inside its body. In one moment its plantigrade for a reason and in the other moment its "break" its own legs and become digitigrade".