Will I get better reception switching from ASDA mobile to Vodafone?

I've been on ASDA mobile for years and after a really bad experience the other day in London where I just couldn't get signal, I've decided to switch. ASDA mobile use Vodafone's masts, of course, but they still offer the best connectivity in the UK. So – do Vodafone arbitrarily limit the functionality of ASDA mobile users to get them to switch over to Vodafone's overpriced plans or would my service be the exact same? If it's Voda's service I have the issue with, is my only real option O2?

Thanks for any help.