When you ask the question which Viper will become the most valuable, you should consider that almost all Vipers were made virtually the same. Same interior (with small exceptions of panels, or dash panel, etc) and same paint (except for some with strips), etc. To distinguish one from the other is just a minor change difference. The ACR's are unique in how they were made, but then again a number of them were made for sale to the public. Which Viper was really uniquely promoted by Viper as being unique, advertised as such, and the public needed to pay much more money for that option? In my humble opinion it has to be the original 2006 Snakeskin Viper. (not the green Viper). They were advertised uniquely as a special edition, had posters made, had advertising and promoted to magazines on what that option was, and worked really hard to make a go of it. It was a $25,000.00 option to the buyer. Special badges and emblems with "Snakeskin" actually under the "Viper SRT-10" badging on the car both inside and out. It had snakeskin seats, steering wheel, shifter, dash panel, roll bars, sun visors, and console (with medallion embroidered). Most amazingly, it has a very special snakeskin paint (hand painted that looks like real snakeskin that's just amazing in quality). The entire car was professionally done as a Snakeskin and the window sticker had an added sheet to show all of that extra work and what you got for your extra $25K. If you've never seen one (which is not surprising, since only 7 were ever made) you'll know it's very unique.