when ur asking about a tuner do you mean the handheld?
if so then you should go SCT
If your talking about the person who'd tune it then IMO best bet is a dyno tune. I see ur in LI look @ Realspeed Automotive and Dan Carlson. Guy is great!! has done all my work.
SCT is the dominate hand held used and supported by the biggest shops. They are both good machines. The key is getting the right "tune" in the hand held to upload to the PCM.
IMO - dyno tune is best. Again if your on LI go see Dan @ realspeed and tell him Dave B sent you.
+1 with bama, I had a custom tune done on my 04 FX4 ranger with the explorer express supercharger, he freed up close to 45 rwhp!....lol yes I had a supercharged 4.0L ranger, and yes it ran the quarter just as fast as a S197 stock. not too bad if you ask me from a little pickup.
Where are you located. The best tunes are on the Dyno every car will be a little diffrent and these diffrences can be fine tuned on a dyno in real time. Find a reputable Mustang tuner shop and put it on the dyno. If you live anywhere North GA Modular Power House would be a good choice.
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Power House Turbo, SCT-X-Cal2, Diablo MAFia, CDC Shaker, CDC Aggressive Front Chin, 3DCarbon Grill, CHE UCA, LCA, Kmember Brace, SPEC 3+ LPP option, AEM Wide band and Electronic Boost Controler, SOS Piller Pod.
Best Tuner for 2008 Mustang GT-CS ?? 
