I swear by 3, never had an issue with them and always the cheapest sim only deals imo
I don't think the deals in that screenshot are their 'advanced' plan which includes go roam etc (Although thanks to Brexit they're bringing back roaming charges next year, well done if you voted for that!!!

)
I left to go to o2 last year as they had a decent deal however found the signal rubbish, went back to 3 as soon as the 12 month sim with o2 ran out
but to be honest, it really doesn't matter who you're with, it depends on who's the best carrier for where you live for the best signal at the best price whether it be Tesco mobile or EE
I currently pay £15/m Sim only on 3's advanced plan, 100gb unlimited mins/texts, could easily get away with 10gb a month, no idea what these people who manage to use 100gb or need unlimited data are doing 🤣