If you're looking to switch networks, I would start by seeing which one has the best signal in your house.
You can get free PAYG sim cards delivered from all the major providers. Try them one by one in your phone and walk around your house, noting which network is stronger.
Beware that many "networks" are actually virtual networks. They run on someone else's signal. For example Virgin Mobile don't have their own network, so you should find out which of the big operator networks they are using.
Balham resident since 2011, Editor of https://bestcommands.com/