Here's a site that might help you determine the age of the bikes, assuming the components are mostly original. My guess is that they are. Click on "component dates" and you'll find date codes for the major component brands you can match to the date codes stamped on your components.
www.vintage-trek.com
My guess is the Bridgestone is from around '84, I have an all-original 1984 Schwinn le tour that has Suntour ARX derailleurs on it. I think the Motobecane is likely a few years older than the Bridgestone. The Bridgestone is indeed the "better" bike, it's a chromoly frame with forged dropouts, whereas the Motobecane appears to have a high-ten tubing decal, and it also has stamped dropouts with an adapter claw derailleur hanger. The components seem to be better on the Bridgestone as well.
edit: I see that Little Darwin already posted the link to vintage trek, sorry-