From all 3rd party testing and personal experience Verizon has the best coverage and reliability and signal strength. You can pretty much ignore the ads. All you need to do is talk to people that have the service, everyone NOT on Verizon has told me that this area or that area is bad, I pretty much never see an issue, even when all other phones around me don't work on other plans.
About mergers making things better, I have never seen a merger benefit anyone outside of the top managers at a company. Car companies merge, they ship car making to other countries, buy cheaper parts to raise profits or lower costs for the stock market and then cars become trash. Every time I hear "better for the consumer" or "increases competition" I laugh.