I have flown PE on over a dozen airlines, including UA and all of the LH group. Honestly, the biggest difference to me is which restroom you have access to. PE with a dedicated lav is ideal, as is access to the J lav; unfortunately, neither of these situations are at all common. One issue you definitely need to consider is that LH-group charges for seat assignments in PE, which can definitely add up for multiple segments and multiple people. All things being equal, OS will be better food and service.