The Guru is the most modern and appears the cleanest of the three. I can see a Columbus decal and it at least has dual pivot brakes. However, it's also notably smaller and I can't tell if it is one of their road models or triathlon specific models with a steep seat tube.
The Gardin looks like it may be from the period just before the split with Rino. It has some sort of Modolo brakes and appears to have the Modolo shift levers. The drivetrain appears to have been upgraded.
The Montini is the lowest recognition/prestige brand of the three. The bicycles were contract manufactured for CBD and sold as a B-brand (some might argue C-brand). I can't recall seeing any above lower mid-range.
Given the apparent discrepancy in sizing, that should be your prime consideration. Drive side photos would probably provide a lot more information.