Class on time up to chief: if classed you gain more crew growth.

class it on time and make shure it has a good fighter base elite or base 12 in fighter

Unless the only function you want from the Seaman is fighter advantage, stay away from an elite.  You want something more with 11s throughout the range of Rep/Res/Engr and of course, Ftr and Bmbr numbers.

A good balanced Seaman is what you want, not a single function elite.

The previous would be mostly true if Seaman have a large noticable effect.
Unfortunately they don't.
In order to get a noticable effect from your Seaman ( say a boosting effect that's 5% or more) you need your Seaman  to have the best possible base stat ( 12 or elite),be boosted and as high lvl as possible ( 120).
Don't settle for anything less than a 12 base stat ( preferably even elite) for the main stat you are trying to boost.