After twenty years of travel, I have my packing down to a science. One small carry-on size suitcase, with cubes inside separating clothes categories (which I still check most of the time), and one small backpack. That is it.

But I cannot begin to tell you how the passengers on my tours agonize over their choice of luggage. Rick Steves believes in the minimalist approach – just a backpack. So how do you choose? When is a backpack best, and when is a suitcase your best bet? Here are some guidelines, as suggested in an article by Thorin Klosowski in his Life Hacker blog.

First, there are a few things to take into consideration. How long is your trip, what will you be doing, what weather might you run into, how much more travel will you be doing when you arrive, what’s the infrastructure like at your destination, and how much do you plan on bringing back with you?

A suitcase is probably the preferred choice when you are heading to just one destination, and you plan on staying there until you return, especially if you can unpack upon arrival.

Small backpacks, which can fit under the seat in front of you on a plane, are perfect for long weekends or shorter trips. Also good for those minimalists out there who only bring travel-specific gear and don’t mind doing laundry as they go.

The Goldilocks choice (just right), might be a large backpack. It would be the size that doesn’t fit under the seat in front of you and must be put in the overhead compartment instead. Larger backpacks are perhaps best for someone who cannot commit to the smaller backpack but doesn’t mind carrying something on their back the whole trip. It works well when you have a diverse, complex itinerary, like if you fly in, then hop in a cab, then take trains to get around after that. Lugging around a big suitcase in this instance would be a pain.

Mr. Klosowski is puzzled by folks who prefer duffle bags. I am in agreement with him in this curiosity.