I downloaded a few figures, v3 and v4 for instance, and I'm confused as to the difference on some of them. I see terms like Dev example and dev foundation, Sae, v3 to v2, and others. Can anyone explain the difference? Is there one in particular I should be using?

It is a bit like motor vehicles, there was nothing wrong with the '13 but now the '14 is out the '13 is considered old hat. Much will depend on whether or not you must follow the crowd and be seen driving the "latest and greatest" or if you prefer to be a creative individualist.

Then again some folks are happy to just insert the key, click once and drive off whilst others take artistic customisation to the limit. Current drivers sport V6 but secretly keep a V4 in their garage.

You are in the driving seat, it is an open road not a one way street.

I can understand the difference between Vickie 3 and 4, but was more curious on what is the difference between the "Dev", or SAE or some of the various forms of the same figure. I open the Vickie 4.2 version and I have Vicke 4.2 Dev, also Vickie 4.2 SAE etc. I think there are even more, and its confusing as to which one would I use.

A Dev file stands for Developer. It is a stripped down version of a character used to rig things like clothing.

SAE usually means it has extra injection channels in the characterc cr2 file, but I am not sure if that is the case on V4.

The one you want to use is plain old Victoria 4.2.

Actually, I'm not sure what the "SAE" version is all about, but V$ had about three or four different versions out at one time, including a lo rez version. V4 is the original, V4.1 was an update and V4.2 was I believe the last update to the figure from DAZ. The DEV rig is a Poser Development  Rig for people who wish to make clothing and props for V4 to wear and use.. That's it in a basic nut shell.

I recall V3 SAE was an update released as part of a Special Anniversary Edition bundle.

If you have Poser 9 or higher there are weightmapped versions of both, which have immproved bending... 

V3WM

http://basicwiz.com/VICTORIA-3WEIGHTMAPPED.zip

V4WM and the Outfitter clothing weightmap transfer utility..

http://www.runtimedna.com/Poser-Place/

The V3 to V2 version of Victoria3 allows her to wear clothing & to use poses made for V1-V2, and to use the texture maps designed for those figures, but has the head morphs of V3.

V4 to V3 version does the same but for V4-V3.