April,
Although you may only be carrying your Backpacks a short distance from the station to your hotel, it's important to have the packs properly fitted according to torso length, so that most of the weight rests on your hips rather than your shoulders. Any competent sales person can do the measurements for torso length. Your profile doesn't indicate where you're located, so I'm not sure what stores might be available in your area.
Here are some of the features that I consider to be important.....
- Panel load design - the main compartment opens completely so it's easy to load and one can access the contents easily. The other version is the top-load design which means if you want to reach something on the bottom, you'll have to dig through all the other contents.
- Detachable Day pack - many of the travel Backpacks have a detachable day pack, which is great for a carry-on when the main pack is checked.
- Stowable harness system - many travel packs are designed with a harness system which can be stored behind a zippered panel, so that the straps don't get caught in airport conveyor belts.
Some popular brands of travel backpacks offer separate designs for men and women. One other point to mention is that I would NOT recommend using a wheeled backpack, as the wheels add weight and also reduces the available space slightly.
Two brands of good quality packs are.....
One thing you'll need to give some thought to is the capacity that each person wants to use. Keep in mind that you'll be carrying whatever you decide to pack as well as hauling your gear off & on trains, so packing light is a good idea.
Regarding "do's and dont's", if you're wearing the pack in crowded spaces, you'll need to be aware that if you turn suddenly you could whack someone with your pack. Also if travelling on boats (such as the Vaporetti in Venice) you'll need to take the pack off and place it on the deck.
For longer European trips, I use both of the brands I mentioned above. One pack is slightly larger than the other, so I choose which pack to use based on the specifics of the trip. For shorter domestic trips, I use Tom Bihn or Red Oxx luggage.
If this is your first trip to Europe, I'd highly recommend reading Europe Through The Back Door prior to your trip, as that contains a lot of good information on how to travel well in Europe and includes information on packing.