If you have a pair... gunners... if just one.... meh.. anything really...

anything...its +18

only fighter engineer or Seaman  . Dont use it on gunners , coz on 120 level you get cap on reload and accuracy even with 109 vets . Fighter , seaman , engineer  ability still no capped , so go for either one of these ;)

Yes:

Fighter or Engineer or Planesman or (Repair-nation and state of crew dependant)

No !!! :

Seaman, Gunner, Restorer, Bomber/torper, Scout, Torpedoman etc

If you want a light as possible crew gunners would be a good choice.

There is a small chance that a X sailor can reach the last range upgrade sonar gets, before the elites where unable to reach those caps.

Suck sailors NF X 
i use one as fighter RM 125 lvl  vet 260 nad play like 90 lvl 
NF make many sailors for event but dong giving to sailors true abbility.
Fighting abillity 4700 but fake.I ask some mod why this and say only vet are importan .

so u mean elite fighters arent better than +9 fighters if they both have let´s say 260 vets?

Its really hard to test, but fighters had a CAP time ago. If they didn't change the code, at certain level (high, far beyond lvl 100), almost any base fighter with more than 200 vets should be capped, having then the same true ability in practice. Cap is still level dependant, so if we suppose caps are still there, a base 9 BVE 125 fighter should beat a X sailor base 18, lvl 115.

In the end, the most important thing for fighters is micromanaging.

Also 1 fighter pilot alone is useless, you should have at least 4. Otherwise you are using your best fighter just 1/4 of the time in the best case, or 1/6.

Now planesman has no known cap, and ships have speed cap but engineer's overheat time is uncapped. I don't know about sonarman, but I would go planes or engy.

Thx for all answers!

Most abilities in NF are cap, but you can use these NF X sailors to give good repair as fighter, engineer, bomber, planesman, sonar, etc. (so do not class them into repair).  Usually, the best choice is engineer.  For planesman or sonar, use super elite because they are also +18 (a waste of NF sailor), unless again, you want the +18 repair to help your ss.  Even if fighter is cap (not sure about this), you get +20 repair/s on your ship at 125 level on each of these sailors (vs. super elite fighter that has +6 repair/s), making your CV very durable; 2-3 of these are the same as putting a 125 level repair on your CV and 7-8 of them, your CV will have 200+ repair/s from all the sailors (useful in case you are not careful and get bombed). 

I do not know if planesman are cap or not because when I tested my planesman from around 5 mil true ability to 5.5 mil true ability, there was little change in air refilling time that I measured using a regular digital watch (maybe there is small difference if I used a stopwatch).