Which one do I get to enhance drain and aspir? Has there been any information or testing on it? If I had to guess, I'd say magic accuracy, but I'm not certain.
Enhance Drain and Aspir = Yama's Staff. Also effects Sleep, Dispel, Blind, and other Dark-element spells.
Your options are Magic Damage +4 (25% dmg)/Magic Acc +1 (20 MAcc), or Magic Damage +1(10% dmg)/Magic Acc +4 (+50 MAcc). As these are Trial of the Magian weapons, those stats are open to future development.
Personally, the benefit of that last 15% damage boost from the 4 MDMG affinity Yama's wasn't worth the extra time. Maybe later it will be, and if they work in a way to specify between MDMG and MAcc staves in macros, it will appeal even more; for now the MAcc one makes more sense across the board for Dark-element.
MAcc Yama's still leaves quite a bit of wiggle room in my drains and aspirs. There must be a random number generated and multiplied by your return or something. That said, I notice fewer 'pitiful' drain/aspirs (which may be from resists or extremely low generated multipliers). I have not parsed, taken accurate information, or capped Dark Magic skill yet, those observations are purely my interpretation of things.
I have noticed that the MAcc Yama's is a rock star at sleeping things. Haven't gotten a resist since I picked it up, which is exactly what you want from your Dark staff.