I'll let your vaporous intimations of misconduct on my part pass without specific response.  

One contractor said moisture is coming through a hole in the exterior stucco, but another said no way because the vapor barrier would block it. 1st one recommended installing insulation, but I've also read this can increase condensation problems.

-No smoking, to include cigarettes, pipes, cigars, or any other tobacco smoking material, and/or vapor like products is allowed within the structure of the building; including the rental unit, basement, or garage, either by the Tenants or their guests.

An old garage slab will not have the correct steel, concrete PSI, or vapor barrier that is required nowadays.

Crawl space: have a vapor barrier and ventilation and no standing water (gutters and grading)Attics: no roof leaks and ventilationBasements: sump pumps are good and keep water away (gutters and grading) I don't love finished basements because you can't see if walls are taking in water.

3) Are insulation rolls with vapor barriors the most ecomical way to go?

You ALWAYS - no matter the floor want to put a vapor barrier between the underlayment and the floor material. 

Otherwise, it's a "harmless" water vapor not FDA regulated way of taking in flavored nicotine. 

This reminds me why I do not do residential anymore for investing and only commercial.Had my fill of nut ball tenants and not looking to re-experience that anytime soon.The carpets you can put in a vapor barrier between carpet and padding where it will usually keep from getting to the subfloor.

We recommend 6 mil poly moisture vapor barrier, TrafficMaster Basement Proofer (available by special order only) or RedGard®.When installing Allure flooring in a basement, you must use a basement proofer or a 6 mil poly moisture barrier.