The Logitech c920 is simply the best webcam available.
Anything cheaper will come with a distracting drop in quality, anything more expensive and you won’t notice enough of an improvement until you start shooting photos or video with a proper camera.
Logitech's software is definitely worth downloading, though.
The c920’s auto image adjustments are top-notch when adapting to different levels of light, but the white balance and saturation may take some fine-tuning.
The more recent c922 webcam was meant to replace the c920 in Logitech's line-up, but I'd still recommend the older model over it.