It's probably not the answer you want, but all of those things contribute. Certainly tires are usually the single biggest bang-for-the-buck upgrade you can make to practically any car, so that's the place to start. Unfortunately, the 19"s are saddled with what I would say are only OK all-seasons. They're a great trade-off between rolling resistance and performance, but if you want more grip, you'll need a true summer tire.
Ultimately, the only one that can really decide is you. There's no obvious answer, and each of the choices have their downsides. If it helps, I prioritized a stable, predictable, communicative ride above all else (flexibility in ride height, ride comfort, etc.) and ended up with the configuration in my signature.
So your signature says P85 with Coil and 19's, right? So did you replace the 19's that came with the car to a summer tire? Would you consider a size other than 19?