I've been on a few of the UKs different networks and I have found vodafone to be the best for overall experience when roaming . Most other networks such as O2 & EE drop down to 3G or 2G when making a call abroad unless in countries with those networks switched off, however out of the 6 countries I have been with Vodafone there has been 4G calling.
Also I think vodafone should update their Roaming Checker as they have 5G roaming agreements in countries which aren't even listed as having 5G roaming so thats a big plus even though not essential.
