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I would say the STL based off the no info you gave...
The TNK is more of a pipe ski to me, it's just a bit stiffer than the STL but has the race base which the STL doesn't, the pop on this ski is incredible and it's a fantastic park ski.
The STL is simliar to the TNK but is is much more playful, it's not a lot softer and defintely not an Invader, but has a different kind of flex to it. It doesn't have the race base, which does make it more durable on rails. To me this is more of a park ski and the TNK a pipe/comp ski
But in all honesty they are both fantastic skis and you won't make a bad choice, just have to decide which ticks more boxes for you, if you want a more personal view for you, then give us some info on your ability size and all that jazz.