This.
Then VII, then, IV.
I think VI and VII integrated some of the best balances between class definition and customization, while IV brought static classes definition to another level.
I liked playing X a lot, but the ending was terribly disappointing.
IX was just a combination of what worked in the previous games. It was fun while playing but like fastfood, it left a feeling of dissatisfaction once it was finished.
XII was fun and had an innovative game play and character progression, but the game was just a purpose for a massive sidequest that took predominance over storyline.
It's hard to compare XI with those. It feels like an online version of FFIV, with predefined classes that earn abilities at specific levels without much customization outside of gear.
I could see FFXIV having a similar progression over FFXI the same way FFVI and VII progressed over IV, as they are already trying to improve customization.
All they need to do, IMHO, is to find, and lock, what defines the most the different classes. In VI it was innate abilities and natural stats (before messing with the espers), in VII it was limit breaks, which is more or less the ancestor of weapon skills or TP moves.
