Receiving three regions here I've seen a mix of both over the years and on the whole the single headed programmes have been stronger. Most regions still have sports and weather presenters so there are other people for them to interact with.
I guess though in ITV's case where most of the news teams now pre-record another bulletin beforehand there are benefits in having the shows co-hosted.
If other ITV regions are anything like West Country, then ITV English Regions probably
need
the "banter"-potential that being dual-presented brings - just the help fill out their 30 minutes of airtime!
Often most/all of the stories on a typical evening strike me as "human interest fluff", whilst totally missing stories covered by BBC Points West that I would consider to be more "proper news" (or relegating such stories to one-line-each mentions during a quickfire "other news" roundup, as if it's a GMB bulletin).
Such stories as they have ("proper" or otherwise) are often each padded-out to the max - e.g. the main report package, then some generic info/statistics etc about the issues raised by that same story in more general terms, then an interview with someone who has the most tenuous connection with the story (i.e. an "expert" in whatever the relevant field is, but who has no connection to the specific individual(s)/events/location involved).
Then there's all the multi-region "aggregate" feature items, the protracted pre- and post-weather banter... etc etc etc.
With all of that, the actual total number of different stories covered per 6pm programme seems to be significantly fewer than on the corresponding BBC regional programme.
The first two words of the phrase "Regional News Magazine" can struggle to seem like a justifiable description of what is actually being offered up on screen.