Pre-tax vs post-tax contrbutions to 401(k)?

Depends on your financial situation. Ask a financial adviser.

There's always a chance "they" could take away the tax exemption behind your 401k -- hence why I'm not that big on 401ks as a fallback to a pension.

Seek a financial advisor to help you understand the options.

This is really important and don't listen to anyone in a forum or try to figure it out yourself.

Post-tax is always better, because the money's already been taxed, and thus, minus whatever taxable interest the money may have earned in the 401k, it's all yours.