Funny - my wife and I had the grinder-sub debate last night.
I grew up in southern Rockingham county and everyone over the age of 30 called them grinders. Sub gained traction prolly in the 1980s at some point. Most of the people my age (late 30s) and younger call them subs. (I'm linguistically conservative and still stick with grinder).
My wife, OTOH, grew up in the Union/Brookfield area. She said she's never met anyone who called them grinders until she met me a decade ago.
I told her it was because the local population shunned ethnic food until relatively recently. As such, a localized term like grinder didn't have a chance to take hold until after the mass media made "sub" the default term.
Of course, this led me to ask if growing up they called pizza saucey pie with cheese. (My back is still kinda stiff from sleeping on the couch

)
Anyhoo, back to the OP: for the seasonal/vacationers amongst the forum who have a presence in the Alton/W'-Tuftonboro area...if your travel takes you down Rte 125 in Plaistow, make a point to stop in at Danos. I have no specific recommendations. It's all good.