I love my Eagle Creek Switchback 25. It is two bags in one, always handy. It's freakin' indestructible. While I rarely need to convert the suitcase to giga backpack, this summer in London when I got into a hotel, lovely typical English place with a small staircase and no elevator, boy, was I happy to not need to haul 25kgs up two floors in my hands.

Yes. It's not the lightest. Physics apply.