Starbucks most of the time. If I'm up for regular coffee and have planned ahead, I'll drink my cold brew from home.
I really enjoy iced espresso drinks (well mainly lattes) and Starbucks rarely disappoints. I generally just get plain or with extra shots, but I had my first Pumpkin Spice Latte today.
Dunkin' Donuts is kind of awful for me on iced coffee. Their coffee in general is always really weak.