The bag you choose decides how your trip feels before you even leave home. Pick a 70L checked behemoth and you'll bring 20 things you don't need. Pick a 28L backpack for a 3-week trip with kids and you'll be miserable. There is no single "right" bag. Only the right bag for the trip in front of you. Here's how to actually decide.

The three real categories

Forget marketing labels. Every bag falls into one of three buckets.

Carry-on only (20–45L)

Stays with you, fits the overhead bin or under the seat, and never sees the cargo hold. Best for trips up to 2–3 weeks, work trips, and anywhere with tight connections or unreliable handling.

Checked (50–90L)

Goes under the plane. Best for trips longer than 3 weeks, gear-heavy travel (skis, dive equipment, climbing gear), family travel where you pool luggage, and any trip with a single long-haul flight and no connections.

Hybrid (35–50L expandable, or carry-on + checked combo)

Bags designed to be a carry-on outbound and a slightly-overstuffed-but-checked bag on the return, or a carry-on backpack paired with a small checked duffel. The most flexible system for travelers who shop, bring gifts, or don't know exactly how much they'll bring back.

The honest trade-off table

Every choice costs something. Be honest about which costs hurt you most.

Carry-on costs

  • You will not bring liquids over 100ml. Period.
  • You'll wash clothes mid-trip on anything over 10 days.
  • You'll fight for overhead space on full flights.
  • Some budget airlines (Ryanair, Wizz) now charge for full-size cabin bags. A 40L will cost you €25+ each way unless you have priority boarding.

Checked costs

  • $30–80 per flight in fees on most US and budget carriers.
  • 30–60 minutes added to every arrival waiting at the carousel.
  • ~0.5% chance of being lost or delayed per flight segment. Multiply by your connections.
  • You will pack things you don't need because you have the space.

Hybrid costs

  • Two bags to keep track of.
  • Often the worst of both worlds if you don't pack with discipline.
  • Slightly higher upfront cost, you need both a quality carry-on and a packable duffel.

A decision tree that actually works

Answer these in order and the right bag becomes obvious:

  • Is the trip under 14 days and city-based? Carry-on. No exceptions.
  • Do you have 2+ connecting flights? Carry-on, or you're playing roulette with your bag.
  • Are you bringing specialized gear (camera body + lenses, ski boots, etc.)? Checked, with the fragile gear in your carry-on.
  • Is this a family trip with kids under 10? Checked, pooled across the family.
  • Will you definitely shop or bring things home? Hybrid: carry-on out, checked back.
  • Are you moving abroad or doing 3+ months? One checked bag plus one carry-on. Not more.

Spinner vs backpack vs duffel

Format matters as much as size.

Hardside spinner

Best for: airports, hotels, anyone with back issues. Worst for: cobblestones, stairs, anywhere without paved streets. A polycarbonate shell from Away, Monos, or July (or the budget-killer Amazon Basics version) lasts years.

Travel backpack

Best for: multi-stop trips, public transport, anyone who walks more than 500m between hotel and station. Worst for: business travel where you look ridiculous wheeling into a boardroom. The Peak Design Travel Backpack, Tortuga Travel Backpack, and Osprey Farpoint 40 are the proven winners.

Duffel / rolling duffel

Best for: trips that mix flights with road travel, family overflow, soft sport gear. Worst for: anything you want to unpack and live out of for more than a few nights.

Sizing rules to memorize

  • US/Asia carry-on: 22" x 14" x 9" (56 x 36 x 23 cm)
  • European budget airline (strict): 55 x 40 x 20 cm. Buy to this spec or pay fees
  • Personal item: 18" x 14" x 8" works almost everywhere
  • Checked: Total linear inches under 62" (158 cm) to avoid oversize fees
  • Weight: 23 kg / 50 lb is the global checked sweet spot; cabin limits range from 7–10 kg

The buy-once approach

If you're going to own one bag for the next 5 years, make it a 40L carry-on with a clamshell opening and high-quality wheels or a comfortable harness. Add a packable duffel ($30, 60g) that lives inside it for when you need to convert to hybrid. That's a system that handles 90% of trips without ever having to rethink.