If the silicone is thick, then silicone > TPU. If the silicone is the same thickness as a TPU case, then TPU > silicone.
Thick silicone: It is a soft material, so it would absorb the impact quite well, basically being a squishy pillow. The thicker the silicone is, the more effective it is. It's not very good at repelling an impact (unless it's thick and allowed to recoil), but is quite good at soaking them in.
Same thickness as TPU case: The extra added rigidity of TPU would be better at repelling an impact vs silicone which would still absorb/compress as it normally would. Since it is very soft, the phone would absorb quite a bit of the impact. A TPU case would be better at minimizing it.