What about when you actually need it? Popping it blindly isn't necessarily the smartest choice unless you're just diminishing some AoE damage.
"Best" is highly debatable. I wouldn't give up TS for almost anything after realizing how amazing it is.
"Oh hey, Kor'thik Strike..." *TS* *Goes to 10% HP* *Back to full*
I feel like that 25% nerf to it in 5.1 is what killed it for me. It doesn't feel worth the global without some trinket proccs, and I don't want to sacrifice a global DURING trinket proccs.
It either should be buffed back to original or taken off the GCD. It only blocks ~70-90k (without proccs) every 25s atm. TS can heal back up to H-1 (where H is your health pool) every 25s, and FG will block low-damage attacks by 30% and higher damage attacks by 4-6k (which isn't that strong, but it also doesn't waste a global and scales with your SP).