Ortlieb E-Mate is my favourite pannier. It is extremely well suited to carry commute related stuff. Ortlieb panniers based on QL 2.1 are universal, easy to attach to the rack and can be removed with a single hand pull. The E-Mate can be carried on a strap when not on the bike. There's a word of warning though: even if Ortlieb panniers are equipped with adapters to match different size of rack tubes, these unfortunately rub the paint off the rack. I have solved that issue the following way:
The Ortlieb pannier has two adjustable top attachment devices: I adjusted them the way they sit inside two perpendicular rack beams, so the pannier cannot slide forward or rearwards of the bike. Then I used a good soft tape to protect the paint and make the rack attachment points tubular. As an Ortlieb pannier also has an adjustable hook at its bottom, I protected the rack stays with the tape, too.
After all these actions, the E-Mate sits tighly on the rack with no movements whatsoever. (I will try to post photos after I can get to my e-bike, as it is now packed inside my car).