What video connector for a mid-2012 macbook pro to External Monitor
The best connector is obviously one which matches your monitor.

If you are getting a new monitor, most now use HDMI.

HDMI and DVI-D are very similar, and dual adaptors are common. The main difference is lack of sound on DVI.

VGA is an analog connection, and effectively obsolete, but you can get VGA adaptors for a Mac.