Most people want a straight answer to this, and most advisers who give one straight away are guessing. The honest starting point is that a fixed rate and a tracker are not better or worse than each other. They do different jobs, and the right one depends on the household, not on where anyone thinks rates are heading.
A fix does one thing: it removes surprise. You know the payment for two, five, or ten years, and you can budget around it. A tracker follows the Bank of England base rate by a set margin, so the payment moves when the base rate moves. You take on the uncertainty in exchange for the chance of paying less if rates fall, and the risk of paying more if they rise.
Start with the household, not the forecast
The first question is not "where are rates going". Nobody knows that, including the people paid to say they do. The first question is how much room there is in the monthly budget if the payment went up by a few hundred pounds. A family stretched to the last fifty pounds should think hard before taking a payment that can move. A household with real headroom can afford to carry that risk and may be paid for it.
The second question is how long you expect to keep this mortgage as it is. If you might move, repay a lump sum, or change the loan within two years, a five-year fix with a large early repayment charge is the wrong shape, however good the rate looks. The exit terms matter as much as the headline number.
The number that gets ignored
People compare interest rates and forget the fees. A lower rate with a large arrangement fee can cost more over a two-year deal than a higher rate with no fee. Work it out over the actual term you will hold the deal, fee included, not over a year. On smaller loans the fee often decides it on its own.
There is also the early repayment charge, usually a percentage of the balance that falls each year. It is the price of changing your mind. If there is a realistic chance you will want out early, that charge belongs in the comparison from the start.
A reasonable default
For a household that values a steady payment and has no plans to move soon, a fix of two or five years is a sensible default, with the length chosen to match how long they want certainty. For a household with genuine spare income and a tolerance for the payment moving, a tracker with no early repayment charge keeps the options open. Neither is clever. Both are defensible, which is the point.
What you should not do is pick the option that happens to be cheapest this month without checking that it still suits you if your circumstances change. The decision that is still right in five years is worth more than the one that looks best today.