Hi Joe
I've walked both the Ways, and am the author of the RR guide to the
Kerry Way and joint author of the
Wicklow Way. In my opinion, there's no contest: the Kerry Way wins on all counts.
Scenery: the KW passes close to Ireland's highest mountains, making an ascent of Carrauntoohill unmissable (described in the book). The Wicklow Way does go past Lugnaquilla, but the Lug is tame by comparison. The whole area around Carrauntoohill has the best of Ireland's mountain scenery and is the one place in the country where you can feel quite remote. The southern part of the WW is fairly tedious, some would say forgettable, whereas I can't recall anywhere along the KW for which the same could be said.
Elevation: not quite sure what you mean - there are plenty of ups and downs on both Ways.
Campsites: I think (but am not sure) that the KW would be a better bet for commercial campsites, and for opportunities for wild camping. The WW would almost certainly be more crowded, especially in the area around Glendalough, though you're not likely to see many folk further south. The early stages of the KW, through Killarney NP could be quite busy, but you soon escape into much wilder country.
Trails and roads: unfortunately you never escape road walking in Ireland, but there's less of it on the KW. Having also walked the WHW (which I too thoroughly enjoyed), I can say for certain that there's FAR more road walking on both the KW and WW than there is on the WHW.
Fitness: I think the KW would be more demanding, with a couple of pretty long days, though if you're prepared for wild camping, you'd be in a better position to modify these than if you were dependent on B&Bs or hostels.
Whichever you decide to do, have a great time.
Best wishes, Sandra Bardwell