Advice if you don't mind

[cloudyperpetrator]

Long time lurker

If my DH and I are at the stage where we're paying tax on savings (20%)

....would we be better off putting more money into our pensions (we don't have good pension provision anyway) and have salary sacrifice pensions

....or putting money into cash ISAs (interest rates are so low)

....or something else ?

Why are you paying tax on savings?

Do you have no personal savings allowance?

1. Emergency Fund

This should be accessible instantly. 3 to 6 months of expenses is typically a reasonable amount for an emergency fund. If your job situation is very unstable then you may bump it up higher. So it may be £12k, maybe £18k, not likely to be more so is probably within your personal savings allowance, unless your allowance is really low.

1. S&S ISA

For things that are 5+ years away then using a multi-asset fund within this wrapper can be useful. You each probably have a £20k IsA allowance each year. ISA can be withdrawn from tax free at any point. It goes up and down in value, so there is risk of loss, so emergency fund is first to be spent to try to avoid accessing ISA when market is down.

Pension - this is very long term, depending on your age this may be 30+ years before you can access it.
Tax relief on contributions is great, especially if you are a higher rate tax payer. Withdrawal is not possible until retirement age. It is part of taxable income on withdrawal.
If within 10 years of retirement check with pension provider that they offer UFPLS. This drawdown method allows for only some of the pension to be crystallised each time money is taken, so leaving the rest free to grow. If pension provider does not offer it, look to move the pension. Also look at other drawdown options... some may be suitable depending on your situation... annuities are still ok for some.