Pros
Focus on people, work/life balance, opportunities to rotate and grow, hire/promote from within, healthy team environment in most teams I have seen, good benefits, strong/stable company, very well managed (which I particulatly saw during the 2009 economic downturn), people's opinions are sought and taken into consideration by leadership (anonymous employee surveys), opportunity for one to get stand by plane tickets (since FedEx is an airline), among many other reasons.
Kontras
Company grew very quickly and very big over the last 10-20 years and it's different businesess are not that well integrated (watch out that your job is not limited to a small silo.) Growth in US has been leveling off so there are not as many promotion opportunities as it used to be. There are some though and it's overall a fantastic company to work for.