In any rig, TT or 5er, I like the kitchen over the axles. The axles are at the center of rotation of the trailer so that stuff does not get thrown about as much. The kitchen with its pantries, fridge and cooking and table utensils probaby has the most variable load in the trailer bar the tanks.
That said one would hope that the trailer mfr would compensate for a rear kitchen's weight and variablity since a tail heavy trailer is an unstable traiiler. However, I aslo have a lingering belief in the Easter bunny and the tooth fairy.
We just gave my DD and family our 95 Layton 5er it had the rear kitchen which was nice BUT on bumpy roads and such the sink covers stove top and other items would get tossed around. We now have a center kitchen and have not had that problem since, also I can get in to the fridge and lay down on the bed for a nap without moving any slides with the rear kitchen we always had to move the slide to take a nap after a long day on at the roadside rest areas. Pick the floor plan you like but remember at roadside rest areas it could be fatal to move out a slide. With our old 5er we would try to park where we would not interfere with traffic moving through the area.