The MV2 is the king.
Easy to work on, front controller ports, Stereo Headphone jacks, socket BIOS and stuff.
Any 1-Slot'er will do your job fine, but not all will suit your need the same way.
I tend to think the MV-1B is the most reliable of all ( battery leaks are less bound to happen on these little boards )
from my personal experience. Most of the boards I came across were alwlays running with less general issues than others
( Z80 error, Backup ram error, etc ).
However, it's not as simply to put a UNIBIOS on it, and you have to build a little circuit to make it sing in Stereo.
Any 1A, 1AX, 1FZ, 1FZS will do just fine.
4 Slot'ers are bitchy when it come to power. You really need a decent PSU to make them work flawlessly.
6 slots are to be avoided.