Project Super Sleeper

Okay well I'm starting to look for a new car and i've decided to go with a super sleeper that i plan on modding the hell out of....i want one of those cars that you just look at and shrug off and then when they go WOT, you're confused on how a family sedan could go that fast...i'm not planning on spending more than 15k on the car....and i've narrowed it down to these:

1. 2000 Pontiac GTP (i would debadge this and take off any spoilers etc....make it look like a regular grand prix)
2. 1999 Taurus SHO (same as GTP...make it look like a regular taurus)
3. 1998 Buick Riviera (this would probably be the best sleeper...but the heaviest)
4. 2000 ish Nissan Maxima

ANY OTHER SUGGESTIONS OF THESE TYPES OF CARS WOULD BE APPRECIATED :icon16:

well out of all the cars you listed there i would say the top 2 would be (in no order) the GTP and SHO now these 2 cars are already tuned right from the factory and are quite even, although the GTP is a bit faster, the problem with it is that (atleast where I live) most people will see it and know whats going on under the hood (one of my buddies had one) the SHO on the other hand is allot more limited production, especally for that SHO, now I'm not sure if you are aware but that SHO also was equipped with a 240 hp 3.4 V8 (yip a 3.4 V8 lol) so at full throttle they sound awesome, and it's not terribly hard to pump ponies outta it there are chips exhaust systems intakes and suspension systems, and next to anything else you would want and yes they are quite fast without mods ive seen them say bumper to bumper with a Z28 so possily race fast rwd cars and EASILY destroy ricers lol, but whatever you choose good luck man