Can I get better image quality with a higher focal length or by cropping an image from a sharper lens?
Two well known ways to get better image quality are to use a sharper lens, and to zoom in to fill the frame (as opposed to zooming out and cropping in post). Sometimes there is a give and take between ...
I take macro shots of watches and post them on the web (not intended for printing), typically 640x480px. I've been composing those shots in the 1504x1000px frame so that it shows the required size ...