I think you’re better off going with the more widely used material and manufacturing process. TPU is a safer bet as a more common material. If you go with EPU 40, you’re basically locked into its proprietary manufacturing method, CLIP. I understand that EPU 40 is designed specifically for vibration dampening, but I would be uncomfortable being reliant on only one process or supplier. Since the resin is cured with UV light, it may also show some degradation over time with UV light exposure.

With TPU, you have more flexibility in the manufacturing process. As pointed out, TPU can be manufactured using multi-jet fusion (MJF), but there are also manufacturers who use selective laser sintering (SLS). For now, I say TPU gives you the more robust option.

CLIP is an incredible technology, but I agree, not yet as mature as some technologies for TPU printing.

Regarding guidance on design considerations, the short answer is that this is where you need to iterate. As a starting point, you can try minimum wall thicknesses of 2-3mm, and should always design to avoid sharp corners (to avoid stress concentrations). However, you just have to try different thicknesses and rib details until you find the right blend of durability and shock absorption.