2nd gen mainly because of the amount of detail and shading on each part, I really appreciate the detailed weapons and equipment with unique paint schemes, its a lot of fun to work with for ACDC's. I do have a bit of a time with the limited selection of heads combined with the fact they are by far the most unique in the series, it can be difficult to choose. Teddy bear head, dome head, bird head, beady-eyed mohawk head, helmet head and so on! The uniqueness is not limited to just the heads though, 2nd gen features a strong cast of very memorable parts across all part categories. MoA has some of my favorite frame parts, very cool legs and especially the weapon arms, best weapon arms featured in the series. 3rd gen for sheer volume of parts is great, terrific frame parts, I however dislike the lack of detail and character featured on many of the weapons, I'm pretty much speaking for LR here with its heavily monotone paint schemes (even with weapon paint selection). The shapes of the weapons themselves are fine, for me its mainly an issue of detail and color, just not quite as fun to look at and work with as 2nd gens. 4th gen I have no personal experience with designing. It has some very outlandish looking parts, I hear people say it is difficult to design for 4/FA. The game is of the plastic aesthetic. 5th gen is no fun to design for, it lacks proportions ideal for nombots and I find it very inaccessible. Who wants hanging monkey arms that touch ground and squatty legs of E.T., It's just ridiculous. Can have some fun looks sometimes though...