Pros
The best reasons to work at UPS would definitely be related to the idea of seeing what it is like to work for a company that places an extremely high value on efficiency and technological advances. The company studies literally every single element of the business to ensure things are happening as efficiently as possible. Some examples include: UPS employees all use the same ink pen developed and designed by the companies industrial engineers which opens and closes about a tenth of a second faster than the standard retractable pen, they count the number of steps a driver takes during each stop, and they're willing to spend millions of dollars improving legacy technology.
Cons
There are many downsides to working at UPS. First, it is a very difficult working environment to adjust to if you are not already used to a very militaristic working environment. Second, the pace is very fast and every job (from the entry level positions to top management positions) comes with extremely high performance expectations. Lastly, and this one highlights the reason I left the company, it is extremely difficult to move into Full-Time management if you are not a minority or a female. So, if you are a white male who wants to advance in management you had best look elsewhere. During my tenure there it was not uncommon for over qualified white males to sit for years in the promotion pool waiting for opportunities while lesser qualified minorities and females were promoted in a manner of months.