Seat
Premium economy generally provides more space and recline than economy. Long-haul business class may provide a lie-flat seat, but the actual product varies by aircraft and airline.
Cabin guide
Premium economy vs. business class: when is the upgrade worth it?
The right answer depends on more than the cabin name. Flight length, seat type, schedule, price difference and which segment actually receives the premium cabin all matter.
The biggest differences
Price
Instead of using a fixed rule, compare the incremental cost of each cabin against the comfort and time benefit on your specific itinerary.
Flight length
The longer the premium segment, the more meaningful seat comfort and sleep can become.
Mixed cabins
Always check the cabin segment by segment. A short premium segment should not disguise a long-haul economy segment.
A better way to search cabins
Search the cabin you want, but also compare nearby cabin choices when the price difference is unusually small or the comfort difference is unusually large. This is one of the core ideas behind Wayzuno: flight search should surface worthwhile alternatives rather than forcing travelers to think of every possible search themselves.