KB's are nice, Procharger are nice, and Turbos are cool, but to each their own. A Twin Turbo set up is real nice under the hood. I guess its all about what your plans are with the car ( Impressiveness, looks, Daily Driver, 1/4 mile, street/strip, drive it just on nice days etc etc etc...) and where you are at with the mods on it....don't forget PRICE RANGE! lol. Supporting mods are a big benefit to these power adders. Either way you will get great results.
I have been looking the last past few years and decided to go with Procharger. You will get tens of thousands of people saying different things about each....Everyone is looking for something that suits them and wants you to buy what they have or its their first power adder and they will SWEAR by it that's its the BEST and are close minded on a one way street...I love those people (joking)
Some pros and cons about each...not all of the pros and cons, but just a few...
Turbos will have lag when you want the power..not a lot but its there, maybe a sec or two. KB and Turbos may produce a lot of heat under the hood. You get rid of the plastic intake with a KB and add a ton of piping with a Single or Twin Turbo set up. Turbos kit comes with new K member, turbo headers, coil overs, tubular A-arms etc etc etc. Procharger is an easy setup, easy to maintain with better workings and stronger parts than other Centrifugals. Centrif's and KB people have lost their belts or complained about belt slippage. Centrifs wont start making decent power till about around 3000 RPMs. But others may say different things about each. You will get great power out of all at different RPMs. Most of the cons I mentioned can be delt with by one way or another. I, myself, don't want to deal with much right now and looking for just a nice set up.
A D1 Procharger would be best for me...I have a K member waiting to go in. My Mustang already has LT's with Full exhaust, Blower Cams, aluminum intake, Stage 3 heads etc etc etc. So you can see, where I am with mods, a turbo would not be worth while for me. I would have a lot of time and money lost to the parts that I installed. A built bottom end is next for me and maybe a transmission before I spend the cash for a D1.
So if you are serious about a S/C or Turbo, there is a lot of things to read up on and look at. I would only buy a new kit but its all up to you. The best way (IMO) and not all people have the option at hand, is to drive one with each. I like them all and each have a different appeal to me...wish I could have one of each in separate Mustangs lol
GL in you search!