Better MOS in terms of promotion rate and ability to actually do your MOS state side? 88N or 42A?

For 88N its easier to rank up to SGT & SSG but once you make SSG you end up competing with all 88 and may end up retiring as a SSG.

Not sure about 88N but 42A has so many troops in it. It took me 7 years just to make my SGT. If you have good scores I would look at the Intelligence field like 35N that was my secondary MOS to SGT is quick and to SSG is good too. My Buddy I was in the Navy with was a SFC before I got my SGT. So I starting working on moving over to my secondary MOS before I got hurt in Afghanistan and had to retire.

I was a 15Q for almost 4 years and reclassed to 88N, Within 6 months I was picked up for E5. Points have been low since I got in the MOS.