The introduction of flying LCav units in both NA & KoM definitely saw more take up over their respective theme lists - which seemed were previously fairly balanced in take up.
Definitely agree from a model perspective that NA are now way ahead of varangur - pretty much fully covered v a handful of units.
Newer, nicer sculpts and flyers give RFO a big plus over regular orcs.
Ratkin slaves an odd one - plenty of model availability, but only a couple of viable builds and the couple of players who seemed to use them regular in uk events have moved on to other projects.
Dwarfs - de6 and throwing mastiffs is a really strong build, while other lists can do the scouting/pathfinder thing which free dwarfs are strong at?