Sareth,
I'm one of the people behind Ask Mr. Robot. The gems you should use all come down to a bit of math, based off the stat weights. Let's look at the arms stat weights: Strength is 2.25 and Crit is 1.25. Let's say we're talking about +60 STR as a socket bonus. The math would look like this:
--160 STR Gem and Socket Bonus = (160 * 2.25) + (60*2.25) = 360 + 135 = 495
--80 STR & 160 Crit Gem and socket bonus = (80*2.25) + (160*1.25) + (60*2.25) = 180 + 200 + 135 = 515
--320 Crit gem (no socket bonus) = 320*1.25 = 400
As you can see, the winner in this scenario is the hybrid gem. But, it all depends on your stat weights. The weights we get at Ask Mr. Robot as generated from a series of tests with SimC. We wrote a program that interfaces with SimC to test out various sets of gear until it converges on a stable set of stat weights. We also follow top theorycrafters to make sure we keep up to date with the latest theory and update stat weights as needed. However, if at any point you want to put in your own weights, click on the "edit weights" button and go wild! You can also export the results to SimC to see how much DPS you'd do with that setup (click the "export") button.
Just as an FYI, Mr. Robot also takes into account your racials and professions (and everything else possible) when suggesting gems. If you're a JC, he'll suggest your 2 special JC gems. If you're a human, he accounts for your 1% EXP bonus when using the right weapons.
idefiler6 - if you can tell me what you don't like about the tool, we can work on improving it