there is the target div dimensions, the camera resolution and the steam quality - is there a way to make a better "stream" when I know both sides has good internet connection ?
Usually, browser cares about it automatically while publishing WebRTC stream. Browser can start publishing from lower resolution and then raise it to requested one (but not higher). Also, browser can change publishing bitrate to fit the channel. Please read some theory in this article
So you can use channel quality indicator
and republish the stream with higher resolution or bitrate if quality is PERFECT, and with lower resolution if quality drops (and browser cannot handle this itself).
Anyway, the stream is received by subscriber with actual publishing resolution unless stream transcoding is used. The transcoding requires a much of server resources, and is recommended only if you're streaming FullHD stream via a perfect channel for example, and subscriber needs to play the stream with lower resolution / bitrate (playing via mobile network etc).