Ive heard that the curses drain your prayer slower than the equivalent regular prayer. Like protect melee vs deflect melee? Is this true, and are there any other benefits of choosing curses over regular prayers for basic training/slayer/melee training? I have 72 prayer.

I would say the biggest attraction of Curse are the higher level ones, Leech, Soul Split, Turmoil. The deflection curses only deflect 10 damage :(

The fact that curses automatically destroy prayers makes it obvious.

 

Curses = boss hunting win and pvp win.

 

If you have turmoil pvm is for curses too.

They do drain slower but not by much. The only benefits at level 72 prayer over normal prayers would be berserker for slayer tasks to keep your stats boosted longer. If you regularly use 5 or 10% prayer on slayer tasks you might want to stay on normal prayers. To keep it simple, if you pray a boosting prayer on slayer tasks normally don't use curses until you have 95 prayer.

Piety > Leech Attack + Strength + Defence everywhere.

Turmoil > Piety almost everywhere

Leech Ranged + Defence > Eagle Eye for bosses, Eagle Eye wins for training (i.e. low defence)