The useful comparison is the cost of the allowance you will use on a network that works for you, not the biggest data number on the page.
Look at your actual data use
Open your recent bills or account app and check several months, including any month when you travelled or used your phone as a hotspot. Choose some headroom, but ask whether paying for unlimited data would change anything about how you use the phone.
Check whether the plan has limits on speed, tethering or fair use. If it includes data rollover, read when unused data expires and what you need to do to keep it. Small conditions can matter more than a larger advertised allowance.
Compare terms as well as data
A shorter commitment may suit you if your circumstances change or you want to try a network. A longer agreement needs a closer look at the payment schedule and your likely needs across the term. Read any planned price changes before ordering.
Check roaming for the destinations you visit, including the allowance and any daily charge. If you rely on Wi-Fi calling or want an eSIM, confirm that both your handset and the specific plan support it.
Keep the switch organised
Check coverage at home and work before choosing a network. A prediction is a guide rather than a promise of the signal inside every room.
If you want to keep one UK mobile number, request a PAC by texting PAC to 65075 and follow the new provider's instructions. Check your current commitment and any separate device payments first; changing the SIM plan does not automatically settle a handset balance.
Questions before you compare
Do I need a new phone for SIM only?
The point is to use a phone you already have. Check its SIM or eSIM requirements and compatibility with the chosen network and plan before ordering.
Is unlimited data always worth paying for?
Compare the cost with an allowance above your normal usage. If you rarely approach that allowance, unlimited data may add little value for you.