Depends on your gear and what you're trying to accomplish. If you don't have PDT-50 from gear, you'll need to use a PDT Atma or two; but, given that PDT Atmas give only small amounts of PDT that count towards the gear cap of 50%, while Atmas for virtually any other purpose give you much larger boosts than you can get from equipment, it's always best to cap PDT- via gear. If you can't cap PDT- from gear, you're pretty much chained to PDT- Atmas, which is a pretty large handicap inside Abyssea.
Once you've capped PDT- from gear, there's 4 main builds to consider; melee, nuking, defense, or evasion, depending on the situation.
Melee: Apocalypse, Razed Ruins, Alpha & Omega
Nuking: Minikin, Beyond, Ultimate
Defense: Vicissitude, Aquatic Ardor, Mounted Champion (DEF+50 VIT+50 Regen+35 Absorbs damage) is what I use.
Evasion: Cloak&Dagger, Siren Shadow, Sand Emperor
Of course there's many combinations for many situations, but this general outline is the best I can do for you without more information.
RDM can attain an almost static 50% reduction to recast time, SCH can over shoot this for a total of 60% reduction under Alacrity (provided you are wearing loafers and keeping dark weather on yourself)
MACC is a joke, any job with access to mage gear can hit close the MACC cap on legion mobs, which is why my BRD/RDM can land slow/para/blind despite having only 150 skill (from /RDM.)