I think that *nix commands can be split into roughly two groups: ones that feel like generic "actions" and have multiple implementations (ls, cd, cat), and ones that refer to specific pieces of software (curl, emacs). The first category should be aliased to the PS equivalents, while the second should be left as-is.

With commands like ls, I'd prefer to have my muscle memory get me the first-class Powershell experience (which means a structured list of files, not a string containing ls's output) instead of attempting to act exactly like ls acts in bash. If I didn't want to use Powershell's features (which /bin/ls does not support) I wouldn't use Powershell.