Buying an ASX share is easy. Finding one I would be comfortable leaving alone for many years is much harder.
For a genuine buy-and-hold investment, I want a strong business today with plenty of opportunity still ahead.
These three could be best buys for me.

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Pro Medicus Ltd (ASX: PME)
Pro Medicus is an ASX share that has already grown enormously, but I still think its best years could be ahead.
The healthcare technology company develops the Visage imaging platform used by hospitals and radiology groups to view and manage medical images.
Despite winning contracts with some of the United States' largest hospital networks, management has previously estimated that Pro Medicus still holds only around 11% of the market.
That leaves a substantial number of hospitals still available to win.
There is also more to the opportunity than radiology. Pro Medicus is expanding further into cardiology and broader enterprise imaging, potentially allowing its software to become more deeply embedded across hospital systems.
Winning major healthcare customers can take time, but once the platform becomes central to clinical workflows, I think those relationships can be extremely valuable.
That makes Pro Medicus the type of business I would be comfortable holding through short-term share price volatility.
TechnologyOne Ltd (ASX: TNE)
TechnologyOne could also be one of the best ASX shares for a long holding period.
Its enterprise software is used by councils, universities, government organisations, and other large institutions to manage important day-to-day operations.
These customers generally do not change core software systems lightly. Moving financial, payroll, property, or other critical processes to another provider can be expensive and disruptive. That helps TechnologyOne build long customer relationships and recurring revenue.
I also like that the business still has opportunities outside Australia. Its expansion in the United Kingdom gives TechnologyOne another sizeable market to pursue, while continued investment in cloud software and artificial intelligence could increase the value of its products for existing customers.
Overall, I think TechnologyOne has many of the qualities I want from an ASX share I would own for a decade or longer.
REA Group Ltd (ASX: REA)
REA Group is another ASX share I would be comfortable owning for the long term.
Its realestate.com.au platform has become deeply embedded in how Australians search for property, giving the company a very strong position with both buyers and sellers.
That large audience is a major advantage. Property agents want to advertise where buyers are already looking, while buyers keep returning because that is where the listings are. I think that creates a network effect that is difficult for competitors to replicate.
The Australian housing market will always move through stronger and weaker periods, so listings activity can fluctuate.
But over a long timeframe, I think REA Group's dominant position and ability to earn more from its audience give the business plenty of room to keep growing.
Foolish takeaway
I would not necessarily expect these ASX shares to outperform every year.
What I like is that each company has a strong position today and a clear opportunity to become much larger over the next decade.
If I could buy Pro Medicus, TechnologyOne, and REA Group at sensible valuations, I would be happy to hold them for years and give those growth stories time to develop.