Which is better for video calls and remote work?

The M4 Air. Its 12MP Center Stage camera follows you and frames the shot, where the M3 Air has a 1080p camera. Both have three mics and Spatial Audio speakers.

Is the M4 worth stepping up to from the M3?

If you are buying new, yes: you get a newer chip, 16GB memory standard and a newer macOS. If you already own an M3 Air, the jump is small and not worth an upgrade.

The M4 Air, mainly because it starts on a newer macOS release and will get updates for longer. Both are fanless with sealed batteries rated at up to 18 hours.

Do I need 16GB of memory?

For browsing, documents and streaming, 8GB on the M3 is workable. For many browser tabs, photo editing or running virtual machines, 16GB is the safer choice, and the M4 includes it.

Which is better for a bigger screen?

The M3 Air, which comes in a 15.3-inch size. The M4 model here is 13.6-inch only, so pick the M3 if screen space matters more than the newer chip.

Apple MacBook Air M3 vs Apple MacBook Air 13" M4

The M4 Air is the newer machine and the better pick for most people: a 10-core CPU, a 12MP webcam and macOS Sequoia out of the box. The M3 Air is still a strong laptop and its 15.3-inch screen is the one to get if you want more room to work. Reviewers and owners praise both for silence, battery life and build; the M4 is a modest step up, not a transformation.

Choose the MacBook Air M3 if you want the larger 15-inch screen or you find the M3 model in the configuration you need.
Choose the MacBook Air M4 if you want the newest chip, a sharper webcam and the longest useful life from the machine.

Prices

Apple MacBook Air M3: $629.30 at CTT Home & Culinary (last seen Nov 3)
Apple MacBook Air 13" M4: $889.99 at PayMore Valley Hi (last seen Nov 13)
Difference: the Apple MacBook Air M3 is $260.69 cheaper than the Apple MacBook Air 13" M4 at the latest prices (Nov 3 and Nov 13)