I am not familiar with the OBDII stuff that much, but check the OBDMPG thread. One is mentioned in there, and it seems to work with just about all of the front ends and plugins.
As far as the most used / most popular skin.....
That is more a matter of taste. Have a look through the skins, and see what one appeals to you. Do a little reading in the thread, and see if is is complete or has the features that you want.
Not the response you thought I would type is it Enforcer