motorcycle helmets have changed a lot since they first had them. Mostly due to teh Snell Foundation requirements. I only buy helmets with Snell rating apart from teh DOT rating.
I have a HJC (CS-12) and KBC (TK-7) helmet. I use the HJC all the time, the KBC is a spare. They are both full face helmets. I have one HJC open face (CL-5) spare helmet too. THey are all SNELL certified.
IMHO any helmet is better than none. You can buy a 400 dollar Arai or Shoei, but in the end your head will be well protected like one from HJC or KBC which might be 1/2 the price of an Arai. The difference for Arai and Shoei is that they use nice materials and your head feels really comfy. I know when i went to my HJC from the previous Vega model I was basked in luxury. I have tried the Shoei and Arai helmets and as per weight and luxury, but there are comparable to each other. Other manufacturers dont compare in comfort and venting but then i dont have 400 bucks to spend on a helmet like that.
When you buy a helmet, run a tape measure around your fore head, above your ears. That size is your HAT size. Buy it in that size. Check against the size rating for the helmet so you fit in that size. If its tight going in on the head at the store, its okay. Make sure there arent any unusual pressure points on your head (like pressure only on the front). The pressure should be equal. The snug fit, or really tight fit will losen up as you wear it. Also a snug helmet will not flap around in the wind. Between manufacturers there is a shape difference. Arai seems to fit oval heads, shoei the round head. I for some reason cant fit comfy in either.
Hope this helps;