I've recently begun researching these cars as I plan to buy one after I receive my Radiation Therapy license. Originally I was thinking 2015 Mustang all the way, as I'm a die hard Ford guy (at least Mustangs and trucks) and I loved my Mach 1. Anyways, recently had a chance to test drive/compare the two and here are my thoughts.
Some highlights:
Challenger Scat Pack:
-Loved the 485hp 6.4L, great sound. I would say a bit more powerful than the Stang but they are pretty close. MT tests the Scat pack as slightly faster.
-Would buy the 8spd auto but drove the 6spd and preferred it overall to the Mustangs.
-It's a big car! One advantage here is that the ride quality is better than the Mustangs IMO.
-More usable interior, you can actually put people in the back seat with a little comfort.
-Kudos to Dodge on the interior improvements, I was very impressed. Actually liked the Challenger's interior over the Mustangs. The Uconnect will take getting used to, but I enjoyed the 8.4" screen.
-Exhaust sounds great. Very aggressive without being intrusive while cruising.
Mustang Performance Pack:
-5.0 sounds great, but a little tame compared to the '11-14 (aftermarket exhaust needed IMO)
-Shifter was very easy to use, almost too light though. The Challenger had a heavier, more solid feel.
-Better handling/braking than the Challenger as expected because of the weight difference.
-Car looks great in person.
-Interior also vastly improved. There is still hard plastic on the top of the door panel. Not everyone rests their arm in that spot, but a little surprised it wasn't soft touch material. I like the "airplane like" feel of the cabin as well.
-Drove during high traffic time, and this car gets a lot of looks.
Aesthetically, that's going to vary person to person of course. I love the way the Mustang looks, very sleek and sexy. Definitely draws you in when seeing it in person. At the same time, I love the Challengers classic muscle car styling. Reminds me more of a car I would admire as a kid, and aspire to own as an adult.
Price, the Mustang has the edge here. My moderately equipped Scat Pack stickered for $44K, while the Premium PP Stang was $39K.
Much to my surprise and everyone that knows me, I actually preferred the Challenger! I preferred the driving experience; it feels more visceral, and more fun to drive than the Mustang. Don't get me wrong, the Mustang is very nice; quiet, powerful, solid chassis, aesthetically pleasing. It's almost too refined though, as if it's not quite muscle car but more sports car. It absolutely goes when you hit the pedal, but didn't give me the smile I had hoped for. Some will like the way it drives (myself included), but I found the Challenger more engaging and exciting than the Mustang. With the Scat Pack, I couldn't stop grinning; same way I felt with my old modified Mach 1. Even though I drove manual transmission cars, I would go auto because of my wife(I've read the ZF 8spd in the Challenger is fantastic and both have paddle shifters now).
In all fairness, there was no testing in the twisties. When it comes time to buy, I will have to take them out much longer and on varying roads/surfaces.
Final thoughts: Mustang has the win in handling/braking, Challenger's engine, trans, exhaust, and interior are gems. If you want a Mustang that's basically better in every way albeit while losing some of its "muscle", then buy it. Dodge markets the Challenger as a muscle car and I feel that's exactly what you get; a muscle car that is surprisingly comfortable, quiet and eager to play when called upon. For the first time ever, this Mustang guy might go for the competition; a Sublime Green one 
Anyone else drive these cars and want to share their own thoughts?
Pics of the testers:
Anyone else drive these cars and want to share their own thoughts?
Pics of the testers:
I also would buy an 8A, and it's slightly quicker than the manual.
