what is sd tune? what is 2 bar or 3 bar?
what is better dyno tune or street tune?

 

SD tune is 'speed density'...ie 'Mafless'.
A dyno tune will always be better as it allows the tuner to hit speed and load conditions otherwise difficult to do safely on the road.

 

If you aren't forced induction and getting to the limits of your MAF airflow and don't have the ability to tune yourself (at least learn it) I would shy away from doing SD or 2bar. Flamesuit on, it is just not a necessity in NA unless you are making so much power you need to ditch the restrictive MAF tables in older setups.

as howard says, dyno tunes will always be better, but only if done properly with a load capable dyno. Not a 5 minute whollap on the dyno and send you out the door. Otherwise, I'd take a street tune anyday. (again by someone who knows how)