Should thugs fight alone or with bodyguards?

[AfroSquirrel]

As you said, it depends on their role. Against armies, things will vary on a case-to-case basis. Against PD, though, I sometimes send out a couple of 'sturdy' chaff only if my thug needs to do some casting. Naiad Warriors are my personal favorite, having shields to block arrows as well as Awe to block most melee, since PD is generally relatively low-morale units.

[Makinus]

With the caveat that i play exclusively single player, i notice that thugs do better if at least working in twos and with 4-5 bodyguards each.

It is also important to select the right bodyguards: ideally a bodyguard should have high HPs and/or protection, a shield also helps a lot, the rest is optional.

SCs, if well kitted, can work solo without much problems...

You also should not spend more than 2-3 turns in buffs (2 is better) regardless of reinvig, as the problem is not only the fatigue, but the lost turns before the thug/SC starts dishing damage.

Edit: a good strategy for using thugs is attaching another mage to the thug couple solely for buffs, i normally use those independent 1 nature mages for this role to cast small buffs on the thugs (nature has some useful low-level buffs)... I always equip them with some kind of bow, script the last spell as eagle eyes and leave them to fire at enemies...