I'd consider my determination on using the Lower in a long time frame.
I'd want it to be the one that is more comfortable and has the potential for more durable service. You can get through the AR ownership experience with only one Lower, if it's a reliable and versatile one.
Consider the simple fact that you can only shoot one rifle at a time, and that AR's are standardized; so Uppers can be swapped out very quickly. Put your specialization into additional Uppers.
Greg