Whilst SIPPs (Self Invested Personal Pension), Personal Pensions and ISAs all offer tax efficiencies, which you choose to invest in should depend on your personal saving goals and needs.
A key difference is around when you can release your money. With a SIPP or a Personal Pension, any money you invest is not able to be withdrawn until you're 55 or over (rising to 57 from April 2028), whilst ISAs are usually used for more short term goals than retirement (such as saving for a house) therefore funds can be released at anytime. However, Stocks and Shares ISAs are usually considered medium to long-term investments of at least five years.
A pension is a savings vehicle to provide an income at retirement. You may be eligible to receive tax relief at your marginal rate on contributions up to the higher of your earnings or £40,000.
Any income or gains made by the pension fund will be tax-free. When benefits are taken, generally up to 25% of the value can be taken tax-free with the remainder taxable at your marginal rate of tax in the same way as earnings.
Any income or gains made by an ISA will generally be free of tax.