It's good to see that no-one has yet come out with "Only buy a £200 lid if you have a £200 head". Hopefully now that helmets are rated, and we see that cheaper ones can be just as protective as the more expensive, that old canard will be put to bed.
Anyway, as suggested above, you need to just get out and try some on. Everyone's head is a different shape, and each range of helmets tends to only feel just right if your head is the right fit. Having a comfortable helmet that is not going to piss you off is definitely worthwhile.
Once you've decided what you want, then I'd say don't buy from the web. I once did that (the shop did not have the colour I wanted, and I could not wait for them to get one in), and found that the lining had been changed in design between trying and buying, with the result that the new one hurt my ears badly enough that I can't use it. I persevered hoping it would compress a bit, but it never did, and by the time I realised that it was no use for me it was too late to send back. On top of that, of course, it's a bit of a ****'s trick to make use of your local shop's facilities, and then not give them your business.
If you are just looking for personal recommendations, then my Schuberth S1 has been the best helmet I've used so far for all round quality, quietness, and robustness, and the BMW System 6 is the nicest feeling one that I've ever tried on in a shop.