Scavenge is the best one atm, no contest. All of its abilities are good or great.
The others are pretty meh. Luftwaffe used to be a no-brainer but now it's fallen out of favour since the MG34 became non-doctrinal.
Fortifications can be good in certain cases because you can plant mines with Volks and build MG bunkers.
Spec Ops is also decent if you go for Obers.
Feuersturm is also ok if you want flamethrowers on SPio's.
Personally I pick Scavenge 90% of the time, it's just miles better than anything else.
Have a look here as well:
https://www.coh2.org/news/55579/tightrope-s-pacific-invitational-3-a-meta-review