Thanks for all of you who've commented on this even though it's been a bit confusing when I've taken into account other comments & general views about what people expect from a Winamp based install (more so from the few hundred comments, tweets, etc that I've looked at over the last day).
So based on all of that, the best approach with new installs is going to be not pre-selecting the default install skin (unless installing over the top of an existing install or if modern skin support is not present) & go with the preview selection dialog from the first post (which also appeared in beta build #2826) & do the one-time selection by the user as there honestly doesn't seem to be a single way to appease the majority when it comes to the default skin.
The reasoning for this is that although most of the comments from our group is for the Big Bento Modern (BBM) skin (or keeping with the Bento/Big Bento modern skins in general), the wider view point about Winamp is the 2.x classic skin & about the experience being fast to load & lightweight on resources & even with modern hardware, a modern skin is still typically taking a few seconds to full load.
With the preview selection dialog the current ordering of the skins seems to make the most sense as it puts classic & BBM as the preferred classic & modern skin options by default whilst still providing Bento & Winamp Modern as there's still a lot of love for those skins out there. As based on the feedback, BBM seems to be the preferred modern skin but you have an easy way to not go with it so everyone wins
Finally, requiring user input maybe isn't ideal in some eyes but the preview dialog we've come up with covers the commonly expected options as well as educating the user on how to change the skin which is something that was sadly missing from the Winamp provided option & has possibly caused confusion over the years.
Hope that all makes sense & why the decision has been made & I've attached the final version of the preview selection dialog for convenience
-dro