I started with 5, then got 6, 7 and now run CS. It's a toss up between 7 and CS, probably because quality and productivity improved with them along with a better grasp of the many features. I love the Actions.
v 1.0, that brings back some god memories and also SuperPaint as well. I still have PS v 1.0 on one of my CD's if you are still interested.
For me version 3 was when I got a full handle of all the tools and some very quite developed since v 1.0, that being said I prefer v5.5 😀
6, 7, 8, 9, and it shall continue are all nice however it started to be way too bloated after 5.5 and load time started to drag along with other hardware requirements. 🙂
If you wanted to counterfit US Dollars then stick with version 5.0 or earlier. (I'm joking.) Really, the US Treasury mandated that all versions after 5.5 or 6 (somewhere around there) have built in mechanisms to detect when any image of US currency was opened.