I always recommend the OT vokes the spiney right away. Just makes things smoother especially in a DF group. I always MT Garuda EX and knowing the timing of my voke makes things much easier. Especially during twisters phase I know Suprana will be dead by the time I need to voke it off the OT making running to the middle less risky. During plumes phase the OT vokes it and takes it away from the clump so they can be AoEed down. If the OT takes it right away, he will hit 2 stacks right when Garuda does her 2nd slipstream, again making it easier on the MT.

Plus mages and DPS freak out when the spiney is on them.

I still think Garuda MT is the hardest fight to tank. (not that any are that hard) Anything you do to make it easier on the MT will make your farming much smoother.