SF4 = offline has nothing, online has great connection but is often a fireball spam fest, character roster is good, graphics are also good
DOA = offline is fantastic as it has alot to keep you interested, online is often laggy, character roster (and costumes) are fantastic, graphics (and 3d) are the best on the 3DS so far imo.
Tekken = i do not own because fighting games have come a long way since tekken was popular and the fighting is outdated imo.
Blazblue = awful port, if you own a psp then get it for that.
Its basically a toss up between street fighter and dead or alive, both games have solid fighting gameplay so its down to this:
If you want to play online against other people alot - get street fighter.
If you want a game with alot of content - get dead or alive
Please bare in mind they are FIGHTING games, fighting games arnt generally known to have a ton of content so dead or alives tag team and survival and challange mode AND the fact you can view the character models in specific costumes with the 3D and using the gyro to move the viewing angle (for those "desirable" angles) are more than welcome.
Long story short, get dead or alive.