I think we (as consumers) probably have done this to death, still a bit of lively discussion never hurt anyone.
Having used and crashed in a variety of helmets I can say this, you get what you pay for.
The best full face helmet I have used, based on Andy's spec above, is my Arai Chaser.
The best helmet I have worn for protection was the Simpson RX8. A helmet so well put together that when I went flying into the Rover 416 roofline with my head, the helmet had no more than a bit of scuffing, whilst the Rover was written off due to the roof being creased. However the RX8 has a tiny visor aperture and fogs up. Great for summer sun, rubbish any other time. NOT to be confused with the Craft and Bandit copies. I've had a Craft and it was terrible; wafer thin visor, poor lining and thin feeling shell.
I had the misfortune to crash in a Davida Jet open face, and I can say again, that they are great well made helmets. I've tried some of the cheaper legal and illegal open face lids and again, the quality isn't there. But that's why they are £30 not £230.
One of the worst helmets I had was a Caberg J1, it was around the early 00s when flip front's were coming out more. It was flimsy, heavy, fogged up and the visor got scratched incredibly easily. My poor opinion of Caberg's still exists due to two friends having issues with them. One had the pivot screw fall out and the mechanism break, the other had the visor flip open and crack.
I won't have, nor recommend a Caberg again.
So really it comes down to personal choice, you can't predict what will happen to you, you have to go with the choices you make and hopefully not have to deal with them in the worst way possible.
If the laws were different I wouldn't wear a helmet at all for most of the lanes I potch about on, I would on the commute, and I would on longer trips. Again, personal choice but one that's been taken away from us.