The 4th generation Rams (as indicated above) have an great 'true' CAI from the factory. About the only place it lacks, is in the filter (somewhat restricted) and the duct (too many wrinkles to offer optimized air flow), so an aftermarket CAI will normally only benefit the high RPM range.
To answer your questions -
1) Best HP gain - BFI
2) Best MPG gain - All of them will likely cause a 'reduction' in MPG because of the changed driving style. At least that's what the statistics seem to suggest.
3) Coolest looks - This is highly subjective. I personally really like the look of the Volant, and that is one of the criteria that affected my choice.
4) Loudest - Who knows?? I think my Volant is pretty loud, but it's not like I bought 15 different CAI's to compare them on the same truck, and other than a select few, no one changes their CAI on a regular basis, so I don't know if this question can be answered in a qualified fashion.
I installed a premium CAI on my 4th gen Ram and noticed a drop in MPG, and an increase in WOT performance, and a rather undesireable loud throttle sound at any position above 1/6th throttle. AND, I couldn't be happier.
I wanted -
a) Better WOT performance - check
b) Nice clean 'enclosed' look - check
c) Ability to handle future unintended engine mods - check
d) An air filter that will never need service for the life of the truck (in my possession) - check
e) Quiet stealthy operation - uncheck, nada, booooo (But it does sound pretty good.
I got 80% of my 'wants' in the Volant package, and am warming up to the sound.