The answer would be Zero, since they are already an incredibly good unfunded class, but they are locked from Reboot for precisely that reason (or at least that's the only reason I can see).
Either way, what @vacillant said is correct, if you get bored from playing a class for long periods of time, specially mobbing, then that you shouldn't chose that class for Reboot. Other than that, the 'best' class would be a class that is a great mobber and at least either a decent bosser or someone people would like in a party, preferably even with low funds.
So, I'd say... Mechanic, Xenon, Demon Avenger, Demon Slayer, Hayato, I/L Mage, Evan, Bishop, Phantom, Night Lord... It really depends on play style and how you spend your time in Reboot.