My friend travels a lot in different parts of the North West for his job... he was initially on EE and found the signal not reliable in most of the areas he was going to.
He took out a new contract on O2 and found it overall better signal for the locations he was at. Now he's at more different locations and is finding his O2 not the best at these areas but his EE is better lol.
His EE is within the last 30 days. He was going to cancel out his EE but decides to drop it down to the lowest sim only plan as the O2 is a full phone contract.
He really does rely on his phone a lot for his work, some people don't have to go to them lengths but he's found it handy to have.
If you have a dual sim phone it's handy having 2 different networks... its good separating work from personal too.