Material, nib quality and feed are comparable on both models, so objectively no clear quality differences exist; the choice depends above all on the writer's hand. The 146 holds more ink (around a writing day), is gladly handled without cap posted and is thereby regarded as very balanced; the 145 is more compact and better suited for shirt or briefcase, while the 146 counts as a typical desk pen. Recommended is a test in specialist trade with one's own paper, since the grip section of the 145 seems to some too thin, that of the 146 to others too thick. Pragmatically, acquisition of both models is also advised — supplemented with the 149 for signatures.
Related pages on fountainpen.de:
• Montblanc Meisterstück 145 (Classique): https://www.fountainpen.de/c-montblanc-meisterstueck-145-en.htm