whats better for a tank material wise?

[Krindor]

3.2 stat weights from Dervy:
DET: 0.303, 0.303*6 = 1.818
SS (Once at SS for 9 GCD Berserk/ x3 Fell): 0.275, 9*0.275 = 2.475

Skill speed is the clear winner if you're using grade 4 materia.

It's the same for all physical classes except for NIN.

[Kyros]

You are all glossing over his quesiton. SS beats DET on tier IV materia becasue when the DET scaling thing happened they forgot/neglected to scale up the existing DET materia, so you get 6 DET instead of 9.

3.2 stat weights from Dervy:
DET: 0.303, 0.303*6 = 1.818
SS (Once at SS for 9 GCD Berserk/ x3 Fell): 0.275, 9*0.275 = 2.475

Skill speed is the clear winner if you're using grade 4 materia.

It's the same for all physical classes except for NIN.

This guy gets it.

[Alahra]

Skill speed is the clear winner if you're using grade 4 materia.

This is true (except for NIN, as noted). Grade IV Savage Might materia are undervalued compared to their counterparts because Det had a higher item budget value in 2.xx relative to the other stats. That's no longer the case, but they didn't upgrade the old materia to compensate for Det's new relative strength.

The difference is corrected for at Grade V, so that Det is greater than SS.