Not sure daggers are the best choice pre-Mut, but if you're Backstabbing, then slow MH. Post-Mut, it doesn't matter, since the criteria there is which dagger poisons are on and which one has higher DPS, not which hand the daggers are in.
Right now I have 1 crusader enchant and 1 life-stealing enchant available to me, that's it. And I have the above weapons. One dagger is a tad bit faster than the other one. Which weapon should get which enchant?
Use whatever you like, wherever you like it. The best idea is probably to use crusader on the mainhand, since it probably procs more there. And More Crusader = Better. Levelling with dagger pre Mut, you will want to stun your enemies to get behind them, thus not needing much healing anyway. Levelling with dagger before you have mut is probably not the fastest possible, but much fun. And you should probably put the slower dagger in you mainhand, at least that is the classical way of doing it.
Not that any of that would really matter much while levelling. You probably spend more time creating this thread than you would win/lose by having an other combination of enchants anyway. Do what you like, and start killing stuff.