With the exception of Martinez who is quitting, and Voinivich, who I haven't heard of before, the others have been Washington fixtures for decades, Judd Gregg is the best one from NH, the other being a BO DEM, Collins and Snowe have been notorious RINO's all along, Hatch however surprises me, He and Gregg are usually pretty good on this sort of thing.
Gun Owners of America has been around for years, they are the #3 gun organization after the NRA and SAF, you seldom hear of them because they work through the state organizations like GONH (Gun Owners of New Hampshire)
The National Organization has been criticized by both sides of the gun rights issue over the years, My experience is that they don't work with other groups, they excited about things with out checking facts and their information is often days or even weeks behind NRA, dated information is a fault I have also found with the SAF and JFPO web sites as well.
I am better informed by this web site and NRA.