Hardest hitting is subjective and dependent more on ones atomizer. What you are really after is which has the least voltage drop. You'll find that the mechs with silver contacts have the least voltage drop, and then the ones that also have a brass tube will have a smaller voltage drop than their SS tube counterpart. Here are some measurements taken by a member on another forum:
Fast-Tech Chi-You ◦Battery: 4.19
◦No Load: 4.18

Drop: 0.01
◦Load: 3.82

Drop: 0.37
HCigar AIOS T/D Hybrid Chi-You◦Battery: 4.14
◦No Load: 4.13

Drop: 0.01
◦Load: 3.92

Drop: 0.22
Fast-Tech Astro ◦Battery: 4.19
◦No Load: 4.18

Drop: 0.01
◦Load: 3.84

Drop: 0.35
HCigar Brass Nemesis◦Battery: 4.17
◦No Load: 4.16

Drop: 0.01
◦Load: 3.98

Drop: 0.19
HCigar SS Vaperev Nemesis◦Battery: 4.14
◦No Load: 4.14

Drop: 0.00
◦Load: 3.88

Drop: 0.26
Unfortunately the Turtle wasn't amongst them, but draw you own conclusions.