Perfect strike use...

[JoeYounger]

So, with Perfect Strike you roll two d20's and take the better result for one of your attacks.

I'm torn on this. Should I use it to try and guarantee my first attack hitting? Or should I save it to try and get my second iterative attack to hit?

Thoughts? Anyone crunched the numbers on it? I'm not quite smart enough to figure out how to crunch them :P.

[StreamOfTheSky]

It probably depends on how high your first attack's modifier is vs. the foe's AC. If you can almost always hit, rolling a 2nd d20 and taking the higher doesn't improve your (already high) odds of hitting very much. If it's very low compared to the AC, the 2d20 makes a huge difference while as the last attack has such awful odds of hitting that 2d20 won't help much.

Only time I ever used it was for a Zen Archer and my attack mod was pretty high, so I pretty much exclusively used it on the last attack. (Of course, I'd always seem to roll both dice within 1-2 points of each other every time, leading it to almost never make a difference...*sigh*)

If one attack has an important rider and another does not can also sway things. Say you're a VERY high level zen archer (17+) and can now chain Stunning Fist off a bow shot. Making extra super sure that attack hits is totally worth it.

[Chronos]

It depends on your target's AC and your attack bonus. But optimally, you should use it on whichever attack has the closest to 50% chance of success.

[holywhippet]

It depends on your target's AC and your attack bonus. But optimally, you should use it on whichever attack has the closest to 50% chance of success.

Assuming you know what your opponents AC is of course. That might require some metagaming or taking note of which attack rolls hit.

[OldTrees1]

If you hit 50% of the time with an attack, then a second roll increases your chance of hitting by (100%-50%)*(50%)=25%
If you hit 40% of the time: (100%-40%)*(40%)=24%
If you hit 60% of the time: (100%-60%)*(60%)=24%

This is described by Y=X-X^2.
dy/dx= 1-2X
When dy/dx = 0, X = 0.5
So the maximum benefit is when your to hit chance is 0.5 or 50%

[Chronos]

You can usually make a reasonable guess at it, though. If you seem to be hitting a lot, use it on your lower attack; if you're not, use it on the upper attack. On the first round of combat, eyeball it based on whether they're wearing armor, or have a thick scaly hide, or whatever.

[HalfQuart]

Here's the equivalent bonus that 'roll 2d20, take the highest', or Advantage as D&D Next refers to it as:

Roll Bonus
2 +0.95
3 +1.8
4 +2.55
5 +3.2
6 +3.75
7 +4.2
8 +4.55
9 +4.8
10 +4.95
11 +5
12 +4.95
13 +4.8
14 +4.55
15 +4.2
16 +3.75
17 +3.2
18 +2.55
19 +1.8
20 +0.95

Roll = the roll you need to get to succeed
So I'd say use it on whichever attack gives you the highest bonus... if your iteratives hit on a 6 and an 11, then put the bonus on your second attack... if they hit on a 9 and 14, put it on the first attack.