AST is the worst healer still, but it is more than playable now even in savage. You won't be able to do the dps or healing numbers capable of the other two healers but it's still a fun class. Both stances are good, use what you prefer in 4 mans and use what you don't have in 8 mans (if paired with a whm, use noct, if paired with a scholar, use diurnal).
Healers aren't very difficult in this game so there's not that much to it honestly. Just don't spam too much, DPS when you can afford to, use Draw on cooldown, and learn to love aspected benefic.