Diablo III- Skills Article LXXV: The Monk, Defensive Skills- Serenity

Serenity (10 Spirit, 20 second Cooldown): For the next 3 seconds, a protective shield absorbs all damage and control-impairing effects that would hit you.

A more proactive- and self-focused- way of not dying, Serenity is vastly less useful then the first two Monk Defensive Skills- unless you’re alone.  When you’re soloing or toting around a ranged follower, the three seconds of immunity to virtually everything this skill provides are much more useful than a slightly more frequent heal- provided you trigger it at the right time.  If you can get your timing right to use Serenity, then go for it.  If you find that you take all the damage before you trigger it, or you never can manage to take full advantage of the temporary invulnerability, then consider dropping Serenity for something easier to time the use of, like Breath of Heaven.

Peaceful Repose (10 Spirit, 20 second Cooldown): You heal an amount of Life based on your level (at level 60, this amount is 6.2-7.8k).For the next 3 seconds, a protective shield absorbs all damage and control-impairing effects that would hit you.

Of course, you could always use Peaceful Repose and get both benefits at the same time.  In fact, Peaceful Repose is a more powerful heal than any form of Breath of Heaven except for Circle of Life- with the sometimes problematic limitation of only affecting you.  Definitely something for use while solo and not in a party- but very strong solo, as you can use it to both heal and absorb incoming damage in a high-threat situation.

Reap What is Sown (10 Spirit, 20 second Cooldown): For the next 3 seconds, a protective shield absorbs all damage and control-impairing effects that would hit you.    When the shield expires, it explodes, dealing 30% of that damage each, but not more than 100% of your maximum Life, to all enemies within 20 yards.

If you’re especially fond of retributive damage and wading into large masses of enemies, this is a very entertaining rune to attach to Serenity, and one that you can often watch mow down the enemies that you weakened while you were enjoying your three seconds of indestructibility.  Not a bad choice, really.

Tranquility (10 Spirit, 20 second Cooldown): For the next 3 seconds, a protective shield absorbs all damage and control-impairing effects that would hit you.  All allies within 45 yards are similarly protected from damage, and from impairing effects like Frozen and Slow, for the next 1 second.

This is the team play version of Tranquility, and it would not be the least bit surprising if some party members prefer this to the area heal of Breath of Heaven.  Many players are well equipped enough to keep themselves alive and find the control-impairing effects that reduce their activity speed far more of a bane than any amount of raw damage.  Best synonym ever?  I think so.

Ascension (10 Spirit, 20 second Cooldown): For the next 4 seconds, a protective shield absorbs all damage and control-impairing effects that would hit you.

A simple (and minor) increase in duration is the effect of this rune, and it’s really up to you whether it’s worth sacrificing the other interesting effects that runes can give you for a somewhat longer immunity period.  Test this one yourself, unless you’re absolutely and unflinchingly sure you like something better (or like nothing better).

Instant Karma (10 Spirit, 20 second Cooldown): For the next 3 seconds, a protective shield absorbs all damage and control-impairing effects that would hit you.  50% of projectiles and melee attacks are reflected back at their origin attacker.

A faster and more direct version of Reap What is Sown, Instant Karma deals out less damage per target- but in some situations it’s just better, as it helps you kill things before the bubble breaks and thus gives you a chance to prevent even last-moment ranged attacks from getting a shot at you.  This one’s a tossup- pick the effect you like better between this and Reap.