Your first rule for buying a helmet should be:
Is it comfortable after an hour or so on my head?
So how can you test this?
Well, you always have your previous helmet experience to tell you whether you have a Shoei or Schuberth shaped head. But, what if you've seen a new brand helmet which you haven't tried before?
My advice is to go to a good motorcycle accessory/clothing shop and try on the various helmets you like. Once you've found one that you like which also fits your head, leave it on and walk round the shop for about an hour or so. If it's still fairly comfortable after an hour (remember new helmets need time to bed to your head so won't be perfect immediately even in that hour) then you've probably found a good one. Do the same with other helmets. I tend to browse other helmets and clothing while "testing" the helmet. If the shop complains, say you're not going to spend money on something that doesn't fit properly and, if they persist, leave. Someone else will welcome your business.
Many years ago (1988) I invested in an Arai (about $400 - a lot of money back then for a full-face helmet). It was beautiful. I tried it on in the shop. It felt good but, it was only after wearing it for about a hour on the bike that the problems began - blinding headaches. It was pressing against my temple. I learnt the expensive hard way. Always test your helmet first.
My current helmet is a Schuberth C3. It is expensive - very. It is comfortable - like an old pair of slippers, truly! It is the quietest modular helmet I've ever had. My next helmet will be a Schuberth, probably the C3 Pro as it is supposed to be quieter with the addition of vortex generators under the chin piece. Downside is a Sharps Rating of only 3 not 5.
But, remember, you may not have a Schuberth, Shoei, HJC or Arai shaped head.
In the end it is only you who can decide. Your decision must take into account the comfort or lack thereof of the helmet.