Moisture-resistant drywall or cement board for a tiled shower?

I’m planning a tiled shower on an exterior bathroom wall, with 4x4-inch ceramic tile covering the shower walls from the pan to the ceiling. The back wall and one side wall will receive direct spray, while the opposite side is mostly outside the splash zone. I’m considering moisture-resistant drywall with a sheet-applied waterproofing membrane versus cement backer board with the same membrane.

The drywall would be easier to cut, lighter, and probably simpler to finish at the areas outside the tile. Cement board seems less forgiving to work with, but I’m wondering whether its better tolerance for prolonged moisture is worthwhile if the waterproofing system ever develops a small failure.

For those who’ve installed both:

- Would you use moisture-resistant drywall anywhere in the direct-spray area when it’s covered by a properly installed membrane, or reserve it for the non-wet wall only?
- Does the smoother surface and easier finishing of drywall make a meaningful difference under 4x4 tile?
- Are there particular transitions, fastener penetrations, or seams where cement board gives you more practical margin for error?

I’m not treating moisture-resistant drywall as waterproof, but I’m trying to decide whether a fully waterproofed drywall substrate is reasonable here or whether cement board is the safer choice for the shower walls.