Over the years, I had many different employment contracts, with different pension implications. Let's compare them.

PAYE

The bog standard way of working. Decent tax discounts for income tax and NI. Some places offer rebates on employer NI, but i've never received that.

Umbrella Company

This is for inside IR35 workers. You have to pay both sides of NI when working this way, but you save both sides when putting the money into you pension. For example, I am working via an umbrella at the end of the tax year. My income tax will be 60%, employee NI 2%, and employers NI works out to about another 5% (it's 13.8%, but charged before other taxes, so it ends up being effectively less). So I am saving 67% tax on my pension.

LTD Company Director

Nice and easy to operate, I used a Vanguard SIPP. I saved on NI, income tax, and used it to reduce my corporation tax.