There will be a ceiling on all pins but if you can say get a restored MB for the same price as a new Stern LE, it seems to be that MB is the way to go. A timeless, iconic theme, one of the top pinballs ever made, and a fairly limited number made ( 3000 ish ).
I would rather buy a really nice MB than a new Stern. Long term, while impossible to predict, guessing MB will prove a better buy IF the value of a pin is of concern. No real point buying either unless you think you will get real fun from the pin!