Nocturnal is preferred. Those instant shields are largely the reason people are saying AST is OP. The shields have an added bonus of potentially buying you (or your ranged) time to actually cast something, since AB/Stoneskin are the only native spells you have that prevent interruption by damage until they break.

The difference in MND from changing to Fending accessories isn't going to be that high when the equipment is all synced down to i150, and the bonus HP is pretty substantial.

Can't really give advice beyond that. >_>; I only SCH in PvP.