Diablo – Do the shields of Magic Weapon Deflection and Dominance stack

This is just a fancy way of saying "+10% damage for 5 minutes".

Fundamentally, you're looking at the skill wrong - it's not "imbue Target: Weapon", it's "imbue your weapon". If you give it to someone else (soulbound weapons notwithstanding), it's not your weapon, anymore, and presumably you have a new weapon.

Furthermore, since all skills with damage scale off... weapon damage, there is not even an issue of "But I don't use my weapon for X, do I still get the bonus?". The bonus works with all abilities (and includes the runed versions of magic weapon too. Every spell gets lifesteal? Why not!)

You get the bonus. Always. It's a self-buff, and it vanishes when you change your weapon. This also applies to your offhand (should you cast MW on a 1-hander, you lose your MW bonus when you swap offhands).

In the end, it all comes down to your personal gameplay but if you are interested in max DPS my recommendation is using the Magic Weapon (10% more dmg) and using the Force Weapon Skill Rune (which increases the dmg bonus of Magic Weapon to 20% dmg and gives up to a 2% chance to Knockback any enemies hit).