A SIPP is a brilliant way to build retirement wealth, as contributions are boosted by tax relief from day one. But the Stocks and Shares ISA offers something special too: freedom to withdraw your money whenever you like, with no tax to pay. So which is better?

The answer is a little annoying: it depends. So I decided to call in artificial intelligence, to see if it could work out which is better. AI is supposed to be clever, isn’t it?

ChatGPT replied that a Self-Invested Personal Pension offers the instant appeal of tax relief on contributions. “Your investments can then grow free of UK income and capital gains tax.”

Comparing tax wrappers

But there’s a catch: you can’t make withdrawals before age 55 (rising to 57 in 2028). You can then take 25% of your pot tax-free, up to a maximum £268,275. But further withdrawals may be subject to income tax.

Stocks and Shares ISA tax breaks work the other way around. There’s no upfront tax boost, but your investments grow free of income and capital gains tax, and withdrawals are entirely tax-free.

Please note that tax treatment depends on the individual circumstances of each client and may be subject to change in future. The content in this article is provided for information purposes only. It is not intended to be, neither does it constitute, any form of tax advice. Readers are responsible for carrying out their own due diligence and for obtaining professional advice before making any investment decisions.

Those are the nuts and bolts, but no overall AI verdict. So here’s my view. The SIPP gives you a generous tax break right at the start, the ISA at the end.

That makes a combination of the two particularly appealing. It could also help you manage your overall tax exposure in retirement nicely. Now to the next question. What should you buy for your SIPP or ISA?

Aviva offers income and growth

At The Twelfth Magpie, we favour building a balanced portfolio of FTSE 100 and FTSE 250 shares to build long-term wealth. One stock I rate is FTSE 100 insurer Aviva (LSE: AV).

Its shares are up around 75% over five years, but growth has slowed to around 12% over the last year. After such a strong performance, some kind of slowdown was likely.

But Aviva offers more than growth. It’s also paid generous dividends, yielding 6% or 7% at times. With those reinvested, the total return must be heading towards 110%. The trailing yield is around 5.4% today.

Chief executive Amanda Blanc has simplified Aviva by selling eight non-core businesses and focusing its efforts on the UK, Ireland and Canada. Operating profit jumped 25% to £2.2bn in 2025. In the first half of 2026, operating profit climbed another 24% to £1.33bn.

The shares look expensive

There’s plenty of growth potential in wealth management, general insurance and retirement products. The recent £3.7bn Direct Line acquisition adds another growth engine.

Every stock has risks. The cost of insurance claims can rise, stock markets can fall and integrating that Direct Line acquisition won’t be easy.

Today, the shares look expensive, with a trailing price-to-earnings ratio of 27. However, forward estimates put that closer to 15, reflecting expectations for much stronger earnings.

With £20,000 to invest, I thinks it’s good to spread the money across at least five shares from different sectors. Aviva would be worth considering as part of that mix. I’d buy it myself but already hold FTSE 100 insurer Legal & General Group. Sadly for me, Aviva has been the better investment.

Should you invest £5,000 in Aviva Plc right now?

When investing expert Mark Rogers and his team have a stock tip, it can pay to listen. After all, the flagship Twelfth Magpie Share Advisor newsletter he has run for nearly a decade has provided thousands of paying members with top stock recommendations from the UK and US markets.

And right now, Mark thinks there are 6 standout stocks that investors should consider buying. Want to see if Aviva Plc made the list?

Harvey Jones owns shares in Legal & General Group.