Azelf

Of the Lake Trio, Azelf is the only one that is remotely competent as an attacker. However, in this day and age, Azelf's prowess has trailed behind. The move Psychic was buffed to become a good attacking option, improving Azelf's competitors. Furthermore, Mewtwo was released with its signature move, Psystrike, which pulls it far ahead of just about any competitors. When considering Shadow Pokemon - of which Mewtwo is also available as, Azelf is just far too behind.

Best PvE Offensive Moveset

• Confusion is the superior fast move on offense.
• Extrasensory falls behind, but not by much. 
• Future Sight benefits from STAB and is Mesprit's highest DPS moveset.
• Fire Blast lacks STAB and doesn't suit Mesprit's role. 
• Swift lacks STAB and can't be Super Effective vs anything.

Confusion sports significantly stronger damage output than Extrasensory, though the latter generates energy slightly faster. 

Swift is Azelf's cheapest Charged Attack, padding up its otherwise clunky moveset, but it isn't very strong. Fire Blast costs the most amount of energy, but provides useful coverage and can also deal significant damage if unshielded. Future Sight can be used instead of Fire Blast because it is cheaper and still provides a nuke option, though it doesn't provide additional coverage.