[BrRsn]

It really depends on your car, should give a bit more info.

I wouldn't waste money on strut bars, they look really nice in the engine bay but don't make too big of a noticeable difference unless you're tracking your car.

On my jeep I have upgraded front and rear swaybars + endlinks.
The stiffer rear swaybar made a huge difference in performance/handling and was only $150.
Front swaybar made almost no difference, but it looks nice lol.

Lowering springs are generally stiffer so you get less body roll at the expense of ride quality. A good spring/shock setup will lower your center of gravity, decrease 'squat' when you accelerate and decrease nose dive when braking. Accelerate faster, brake faster and can corner faster.