I currently own 2 helmets. Both are Nexx; both made of carbon fiber. I have been using the XT1, but I also have the XR1R. I started with the XR1R due to its very light weight. Its a really basic helmet and its key features are the light weight (lightest at the time and I'm not sure if anything lighter exists yet; 2lb 11oz in a Large) and the large viewport. the big downsides for me were wind noise and the cumbersome visor replacement procedure. The latter was a big problem sometimes on my ride home from work as I would sometimes get caught between light and dark. Switching back and forth sucked. The visor detents also wore down rather quickly.
I bought the XT1 for my commutes, primarily for the built-in visor. Its still a pretty light weight helmet but heavier than the XR1R. The viewport isn't as big either. But, it allows me to run the tinted shade whenever I want so I wouldn't have to determine which shield to use for the ride home. A really nice feature of this helmet is the chin strap. Rather than the typical Double D-Rings most helmets use, it uses a zip tie like mechanism. I can operate the chin strap with my gloves on. It also has a provision for a Nexx specific Sena Bluetooth module which sits quite flush if you get it.
I will be considering one of the Bell Star (pro, race) helmets later this year. Specifically the version(s) that integrates the 360Fly camera. Still not sure when exactly they will release it though. And I would opt for the auto-tinting visor as well.