I've got maximum motorsports stb installed a couple of weeks ago and i've noticed that the car feels a bit tighter in the corners and doesn't flex as much when I drive onto the exit ramps in my parking garage, so it does do something....
But if you really want to stiffen stuff up you should start with subframes. I just did the stb first because it was easier and I didn't want to grind off my undercoating right before winter.
Yup. Do the subframe connectors first. Then if you are so inclined to be the type of driver who likes to push hard through corners you can look into a strut tower brace.
Strut tower braces are easy to install, pretty much a bolt-on affair. The SFC's need to be welded though. They do make bolt-in SFC's but you'll want to steer clear of those.