I have the Medela PISA (backpack style) and LOVE it. I have been pumping 3x's a day since mid-October. M-F I leave the backpack at work in my office and just transport the removable insulated bag to/from work with a cold pack and bottles. That way I am only carrying the entire bag (with heavy pump) to work on Monday and home on Friday (in case I need it on the weekend). If you didn't think you'd ever need it over the weekend you could just leave it at work and not have to worry about lugging it around. But, IMO, it's not that heavy anyway.
I am able to express 4-8oz total in a 10-15 min session and find it is pretty quiet. I clean the parts with soap/water after each use. If I'm running short on time I fill the sink with hot soapy water and soak the parts until I have time to clean them at the end of the day (I have a sink in my private office). If you didn't have a sink you could do that with, you could always fill a plastic container (with lid) with soapy water and stick it under your desk. Or, if you have a microwave at work and wanted to sterilize you could buy the sterilizer bags. That way you'd never have to bring the parts home either. Just the cooler bag.
Mom to two amazing DDs ('07 & '09) and a fur baby.
Gluten free since Nov '11 after non-celiac gluten sensitive diagnosis. Have had great improvement or total elimination of: migraines, bloating/distention, heartburn, cystic acne, canker sores, bleeding gums, eczema on elbows, dry skin and scalp, muscle cramps, PMS, hair loss, heart palpitations, fatigue. I'm amazed.