I have an 06 Charger SRT8, an 09 Jeep SRT8, a 12 300SRT8, and now a '15 Jeep SRT.
You see I am on the 3 year plan
But you see that I am in my second Jeep, has to tell you something.
The Viper is too impractical unless you have another car to drive daily. The Charger and 300 are great and looked at the new Charger before I got the Jeep and to be honest, the interior would've been a step down from the 300. They are better than the first gen but haven't quite caught up with the rest yet. The 300 was an awesome car but I live in Chicago and missed being able to go anywhere in the deeper snow. Now before anyone jumps on me about winter tires....I had a cam, headers, catback, and 3.55 gears with upgraded clutches, winter tires didn't help much.
I've always liked the Jeep SRT, I think it's the best all around...more room for cargo, AWD, sports car performance, looks better than any other SUV stock. Just a great vehicle overall.
After all that, my vote is Jeep.