Posted in that "other" thread. But, believed advised an unbiased view.
Talk to FedEx pilots, as stated in that previous thread, you will get positive FedEx bias. Excepting the 1%. Normal.
Talk to UPS pilots, as stated in that previous thread, you will get positive UPS bias. Excepting the 1%. Normal.
Personally think both will provide you a tremendous career. Both terrific companies that everyone can nitpick till your retire (We will).
As a pilot, your work life will be significantly similar with similar flying type opportunity.
Pilot peers: Same stock and backgrounds. No difference except where they were able to get the job. Good people at both.
ALPA or IPA? Personal opinions will be biased to who they are associated. Neutral to outsiders IMO.
You have friends at both? Guessing talking to those folks would provide a far better gut feeling for you than anything a 'biased' thread posted on either a FedEx or UPS cargo forum.

Nice dilemma. Maybe its too easy. Take first class date. Good journey.