I've been using #GiffGaff's rolling monthly phone and data plan for a few years now and am still happy with it.
Enshitification is creeping, in terms of both pushing you towards options that benefit them, and IMO trying to trick you into pressing the wrong option after you've chosen what you want.
But, sending me a link to check my data usage the day before it renews, with the ability to switch plans to a cheaper one there and then is a very good feature.
When that goes, so may I.

