It depends a lot on head shape. Some are round, most are an intermediate oval, some are very long ovals. The key for helmets is that it fit right - it has to be tight all around the head. With the wrong head shape for the helmet you'll have air either at the temples or front to back (or pressure points in those places, which is uncomfortable and can cause headaches, and still is less than safe). Too many people buy their helmets worrying about fit around the face, but Arai reps recommend you take out the cheekpads entirely when trying on helmets to focus on the fit around the skull. Once that is right, they have a variety of cheekpad thicknesses so you can fit it to the face too. I'm just talking Arai here because they're among the best at providing multiple shell sizes for helmets and multiple sizes on the insides of them to make sure the helmet does its job and is comfortable.
That said, I myself bought a Nolan N104 and have used that now for two years. It's a modular with a massive viewport (so no claustrophobia issues), pinlock antifogging, built in sun visor, great ventilation, fully removable liner so you can wash it when it gets funky (dealbreaker for me there, no removable liner, no sale) - and it's very comfortable. I'd recommend it for anyone with the appropriate head shape (medium oval). I'll probably pick up a new N104 Evo next year and retire this one.
www.google.com/images?q=nolan+n104
The only good way to buy a new helmet, btw, is to going to a brick and mortar and trying them on, preferably with the help of someone knowledgeable at fitting helmets.
http://sharp.direct.gov.uk/ - helmet info and test data on many models.
Price-wise I'd say "what's your head worth to you?". There are places to economize, but your safety isn't (to me) one.