Signals vary from area to area, O2 must be weak where you are.
This is your opinion and it is unfortunate that things have not worked out for you.
For very many of us, the service seems just fine and suits our needs.
@komib94 sorry to hear you didn't get the experience you hoped for with Giffgaff.
All i can think of is you must have poor O2 signal in your area.
Good luck with three but when u need a lot of data giffgaff is cheaper for that