I am looking to do my drain skill.
Which one of the three choices is the best for this skill.
I want to upgrade it so it keeps leveling, no worries about mana use and I don't understand the difference in the other two choices.
pretty much...
you have your choices between Cost, and power.
Cost is good, and so is power.
it depends on what you want it for.
cost isn't as much of an issue with the mana leaching.
but lower cost allows you to use it more often if you happen to be in a nuker party or something...
power is the ultimate, though power increase kind sucks compared to other nukes.
I would suggest going power all the way :)
If you go cost or Sap your drains are going to fail on more often on mobs (and in pvp) your level and even higher more often than if you went power
+1 for power path. BTW, failing magic is not an issue as SirCash indicated, since this has to do with skill's level vs target level. Skill level rises no matter what OE path you follow.