I also have a train / cycle commute (thankfully without the run part

). I was using my partner's Osprey Hikelite, which was a great lightweight bag with great mesh separation from the back but too small. I then started using my Osprey Talon 22, which is my daypack for hiking. I fully intended to replace it with a dedicated cycle pack so as not to wear out my hiking gear. However, I've found the Talon so comfortable that I haven't got round to it yet. I don't have a long cycle but I notice a big difference from when I first started cycle commuting and was using a more fashion-oriented Sandqvist rucksack. The Talon has a helmet attachment so I can keep my helmet on the outside of my bag for the train commute, leaving more space inside for my cycling bits and bobs, lunch and laptop when needed. If I was buying a dedicated cycle backpack, it would be the Osprey Synchro 20.
I hear great things about Deuters but having had solid experiences with the Ospreys have never found a reason to deviate.