New to forum & saw 2 different polls. A year ago, I got a 2012 BOSS 302 Laguna Seca, black with race red accent & paddles. I almost bought Shelby. If I was considering all your options on a poll a year ago, I'd say BOSS 302. It's more fun to drive track ready or not. The Shelby 662 has so much power & traction issue--mine will smoke 'em too, but tires are expensive. All out straight line speed is '13-14 Shelby. Fun to drive like a Banshee--BOSS 302 track pack. They are all fun (V6, GT, Boss, new or old Shelby, and all performance)!!!
Another line of thought, a BOSS 302 naturally aspirated engine (vs supercharger) is cheaper to work on, or pay someone to repair--if dollars matter to buyer. It also allows you to do your own upgrades--turbo or supercharged down the road later.
Today, with new independent rear suspension, I'd say wait & test drive GT350 & let Ford word out the bugs (if any). Let them tweak it for 2017. Then again, I might say "wait" until it comes out with new 10 speed tranny on horizon (2018). Lots of options & depends on your patience level. They are all, fun, fast, and fine looking!!