Moved from the Creative Cloud to the Dreamweaver forum in case other customers have input on this.
By version, do you mean PHP or ColdFusion?
If so, it depends on what you're comfortable with and what the rest of your site works with.
Cartweaver 3 or 4 both the CF and the PHP versions will work. Naturally v4 is recommended as it is a BIG leap forward from previous versions and is continually being updated and new features being added.
If you'd like to know more about Cartweaver specifically it would be better to move this conversation to the Cartweaver user forums - the address is in my sig line below. I'll be happy to answer whatever questions you have.
Lawrence Cramer - *Adobe Community Professional*
PHP & ColdFusion Shopping Cart for Adobe Dreamweaver