"Big power" is less important than a good spread of power.

A shitty laggy old Garrett is sort of the worst of all worlds lol

No doubt you could opt for cams and other stuff as well, but that depends what you currently have etc.

But a turbo is almost a bolt on job, it's easy, it requires minimal effort and will make a good difference everywhere. Don't underestimate what something that spools fast can do to the difference of simply driving the car even without raking the shit out of it. And as a bonus, they'll perform better up top too.