The most bang for the buck and most simple is nitrous. It also has the most risk involved and the hassle of having to refill bottles.
Superchargers/blowers are not cheap but you have power on demand, they are not hard on parts and there are no bottles to turn on or fill. Roots style blowers (the big shiny ones) are less efficient than the centrifugal (hair dryer style) both make big power just in different ways. Neither are very hard to install.
Turbos are excellent power adders they are/can be very efficient. They are a little more of a challenge to package and install, you have to have space. In some cases turbo lag is an issue (which is why they weren't a choice for drag racers until recently). Turboa are also easy on parts.
All three work differently but, pretty much have the same effect. If you are on a tight budget and only want an extra 100HP then nitrous is hands down the easy and only choice. You left a lot of detail out so there is no way to say which is better, it all depends on your budget and goals. All are very effective and have advantages and disadvantages.
There is a lot more to it but, that covers most of the basics. To get the most out of any of them you need to build the engine specifically for it.
well, in just for a streetable car that wont have to run on high octane gas(94 being the highest arround me) i was thinking that a turbo would be best for me, but space being an issue it might not be...and also would it effect the exhaust sound?
Same rules apply that I listed above. Even on 94 octane you still have all three options open. You have to decide what your budget is and go from there. Your budget will make the decision for you. If you don't have $3500-5000 a turbo setup or supercharger is out of the question. For $600 you can have a complete nitrous kit.
Turbo cars are generally quieter some don't even run mufflers.
I have less than $800 in my junk yard dog turbo setup, and it is in an S-10 with a V8. Space is not a huge deal, you just have to get creative and maybe remove some useless items like inner fenders.
Turbos and centrifugal blowers have the most efficient compressors. A properly sized turbo setup will rob little power where a supercharger will always cost you about 10% power to drive it. This hase been heavily debated on the board many times. Do a search for turbo, supercharger, power adder or any combination and you will find hours if not days of reading.
If your going for the turbo check out the mid car mounted version. I think it was in High Performance Chevy this month. They had the turbo mounted where the muffler would go and plumbed it back up front. I wouldnt think this would work very well but they said it actually worked better as it got the heat from under the hood and the inlet air cooled on the trip back to the intake allowing more boost with out detonation. They didnt use any muffler as the turbo had a silencing effect. They had a complete kit and said it could be installed in ubder 2 hours. Would be worth a look.