Obviously, you'd need serious cash (and some moral quality for the other at least) to hire either but it is a no brainer for me: Wolf's Dragoons and Eridani Light Horse. We can argue if there's plot armor in some specific instances and stories (we could also argue that the Dragoons actually go from one highly contrived near destruction to another tbh, but yes arguably they do make it out at the end of each those), but just in general these are very professional, fully fledged military formations that lack typical mercenary problems (both have inherited institutional knowledge of very solid and active militaries at the outset, which then develops into years of actual experience in mercenary operations). These are not units you hire to secure your sister's farm or go blow up some building (and if that's what I'm doing, I'd hire someone else), but to do some serious theater-wide work and to produce large scale, significant military outcomes. They also bring their own unique culture and way of doing things, so you don't get to dictate and micro-manage their operations on that scale, which might be an issue depending on what you're out there doing.
