There is no "best" way, just personal preferences. I just installed my Diablosport Predator Tuner Program last night and played with it some more today. For less than $400 I think it was a bargin. I used the "performance tune" that requires premium fuel and quickened the shifts and firmed them up too. I think just anyone looking for a little performance and just a nicer feel of dirveability should consider this or a similar tuner.
For big HP gains it's supercharging or turbocharging and/or nitrous oxide. I'm not a fan of nitrous if you want increased performance gains for daily driving. Both other methods have advantages and disadvantages which could fill pages and pages here. In either case you need to have a shop that is local to help with the installation AND tuning once it's installed. That alone might force you to decide on one or the other however it seems most shops that do one also work with the other as well. Both will add about the same power in "safe" street applications. There seems to be a lot more properly designed "kits" available for most vehicles in supercharger design because of the simplicity and having to modify only the intake "side" of the engine. Turbocharging requires more packaging and space requirements and heat management issues from the turbocharger. I haven't seen or heard of any turbo kits made yet for the SSR. Hopefully someone else here can provide some additional info.
By the way, my 03 Mustage Cobra is supercharged (all 03 Cobra's are), and I can tell you it's just awesome having a supercharger on any engine! Instant throttle response and with 390HP/390 torque the Cobra has more than enough power and performance to have some serious fun with. It makes my former 2000 6-speed Vette seem slow!
Start your research with these web sites: www.proficientperformance.com
Good luck and if you do either, you will need to start looking soon for replacement tires!