from what I've seen, it seems there are two different head shapes that helmets are made for. I think I fall into that more oval shape. I've had O'neal, Fox (V3), FXR (blade shell), and Shoei that have all fit me well. Troy Lee Designs and the FXR X-1 shell design are more compact and do not fit my head very well.
My Shoei is hands down my favorite. Most comfortable, best venting, and I like that it has emergency release cheek pads for EMS to get the helmet off if they need to someday. It's been my MX and sled helmet for the last several years, and that is what I will personally buy from here on out. I did win a FXR last year and used it for a dedicated sledding helmet last season. It's not quite as comfortable as my Shoei, but is 1/2 the price. The quick release chin strap is pretty awesome though.
I have an older generation Spot and it still works just fine. It uses 3 AAA batteries and I see the new ones use 4. I still get a full season of use on one set of batteries though.