FTSE 100 shares have been bumpy lately but remain a brilliant way to build long-term wealth. Stocks and Shares ISA millionaires swear by them, according to new research from investment platform AJ Bell.

It has lifted the lid on the ‘Super Investors’ who have built up ISA portfolios worth £1m or more. In what is music to this Fool’s ears, they are much more likely to invest in individual stocks than the typical investor.

On average they hold 75% in shares (including investment trusts) and the remainder in funds. By comparison, other ISA investors typically hold just 60% in shares.

Making a million from shares

It’s a brilliant vote of confidence in direct equities, but as AJ Bell managing director Charlie Musson points out it’s a riskier strategy, as their fortunes will be concentrated on a smaller number of companies than if they used funds.

ISA investors are nicely diversified, holding on average 28 different positions. Some hold over 100, while a handful have just a single investment in their portfolios. Personally, I hold 25 positions, of which 16 are direct equities.

Sadly, I’m not an ISA millionaire. But among those who are, oil giant Shell (LSE: SHEL) is the single most popular stock, held by 39%.

That isn’t so surprising. ISAs were launched almost exactly 25 years ago on 6 April 1999, and some millionaires will have held shares in Personal Equity Plans (PEPs) before then. Shell has been a FTSE 100 powerhouse throughout, with an unmatchable post-war dividend track record, until the pandemic struck.

Today it yields is a relatively modest 4.17%, but that’s still above the FTSE 100 average of 3.9%. Consensus suggests it will climb to 4.39% in 2024.

Shell’s shares rocketed after Russia invited Ukraine, and are up 70% over three years, although they’re down 2.65% over the last 12 months. Where they go in the short term will largely depend on energy prices.

I want these shares too

In the longer run, Shell feels like a portfolio fixture, however the energy transition plays out. Now wonder ISA millionaires love it.

Lloyds Banking Group is the second most popular stock, held by 32% of ISA millionaires. That doesn’t surprise me. It’s typically the most traded on the FTSE 100. I was surprised to see 32% held pharmaceutical group GSK. That confirms my sense that this is a stock on the up, and I’m keen to buy it when I have the cash.

Oil major BP is in fourth place, held by 31%, while insurer Aviva rounds off the top five. With National Grid in sixth place it’s clear that serious, successful investors prize dividend stocks highly.

I was interested to see that GSK’s former consumer healthcare arm Haleon in seventh place. It’s flown under my radar. Now I need to pay it some attention.

Scottish Mortgage Investment Trust, Legal & General Group, and HSBC Holdings round off the top 10.

I only hold three of the top 10: Lloyds, Scottish Mortgage, and L&G. I’m red hot for GSK and it’s time I bought Shell and boned up on Haleon. It’s probably too late for me to become an ISA millionaire but I’m happy to learn from those who have.