I'll probably get IDL2, for ease of use.

There are plenty of outstanding light sets, though. The key is whether or not they make use of later features in Poser. The more recent offerings often have additions that take advantage of these new features. Of course, the older ones do not. But, the older ones work just fine, provided you adjust your rendering options accordingly, when necessary.

Two lightsets that I like a lot are CVs Softlights and a Saintfox's light set that I have, but is only listed as "Saintfox Lights" in my directory. It has some fun cels/caustics/masks, IIRC and interesting IBLs. (Both purchased at here.)

Search around the net for Saintfox's freebie IBL lightsets, by the way. There are several of those, IIRC.