openSPOT will tolerate the enviroment in the car much better as it is specifically designed to be a hotspot both in hardware and software terms. You can turn it off without damaging a file system or an SD card, and it boots in about a second, uses much less power than other hotspots (see the specifications in the user manual at
https://www.sharkrf.com/products/openspot/manual/
). We also give official support through email and this forum, and you can find the user manual online.
MMDVM hotspot clones like the Nano Spot use general purpose hardware (Raspberry Pi) which boots a general purpose OS (Linux) from an SD card which takes a long time, prone to filesystem errors, SD card failures and the whole system consumes much more power.
That's my opinion, others are welcome of course.