Ignoring such undefined subjective terms such as 'warm' or 'smooth', and looking at published frequency response graphs for cartridges, it seems to me that they're all coloured to some extent. Most have a rise in high frequencies, some have a dip at around 2-8 kHz before the hf rise. MM cartridges can be corrected to some extent by adjusting capacitative and if necessary, resistive loading, whilst MC carts are pretty much what they are. If neutrality is the aim, then the best suggestion I can make is to have an external equaliser after the RIAA preamp, and correct the frequency response then. Buy a cartridge that tracks well, and has reasonably low distortion and crosstalk, then separately equalise the frequency response.
S
Well stated! This!