Stereo separates left and right. An earpiece paired with a bottom speaker can sound uneven in landscape, while matched dedicated drivers generally make balance easier. Front-facing speakers are harder to cover with your fingers. Bass also depends on driver movement, the air chamber and tuning.
Dolby Atmos can change the sense of space, and Bluetooth codecs concern wireless playback. To judge the built-in speakers, play the same clip at the same distance and orientation. Listen for clear voices, bass, stereo positioning and distortion near maximum volume. Hold the phone as you would while gaming and check whether your grip blocks an outlet.