Speech mapping is a REM technique that uses an inverted (dB SPL (power)) version of the widely accepted ’speech Banana’ as a target.
The actual definition of speech mapping is ‘REAR-speech mapping’ - which stands for Real Ear Aided Response. This gives a good indication of the overall function of your hearing aid in situ, in the presence of speech.
So, in summary they are both REM, but speech mapping is the one you want as it’s likely to give you a good tuning result.
MASSIVE CAVEAT; despite being fitted to target you might not ‘like’ the settings as blindly using REAR without taking account of your personal loudness preferences can be fraught with issues. Also if the average environmental/ambient sound where the measurement is presented differs from the ‘real world’ listening environment, the actual functional gain produced by the clever AI system can/will differ. Your audiologist’s office can’t easily emulate a pub experience for example.