Please be careful. At safecurves.cr.yp.to curves are primarily evaluated with focus on complexity and implementation considerations. There “unsafe” means that the implementation needs to be performed carefully and may be more complex and error-prone than for other curves. “Unsafe” is different from “insecure”.
If you don’t trust NIST curves, Brainpool is for you. I’m not aware of profound critic on Brainpool curves.
Because Curve 25519 isn’t supported by the smart card chip we are using. Also Curve 25519 has the disadvantage that it is hard to protect against side channel attacks when being implemented in embedded devices. From this perspective, NIST or Brainpool may be more secure.
Note that our Nitrokey Start does support Curve 25519, perhaps this is an option for you.