That Black Hawk-KU was going to be my number 3 pick, although it's only barely behind the Hauptmann. To me, the sheer flexibility of the other two (and the breadth of machines they can replace in one go) is more useful. Some of the jobs the Black Hawk-KU does I really prefer to hand to a faster, more mobile chassis in this day and age while a lot of the big mediums are solid enough in design that the OmniMech really doesn't bring enough to displace the Avatar for the purposes of being my only OmniMech. But if I can branch out from one Omni, it's near the top of the list.
And I can definitely understand the reasoning. The Hauptmann is great for replacing your entire Assault force, but by and large, Assault mechs only really fill a handful of functional categories by design, though exceptions do exist. The Avatar, on the other hand, while technically an assault is essentially an excellent high-end heavy. I would justify it more than the Hauptmann on my list. Both excellent mechs, but one more versatile. The Black Hawk, however, I feel could more easily slot into more potential lances and company types than could either. It's an excellent mech for faster cavalry formations, flanking in larger heavy and small end assault formations, spotting for fire support formations, etc. It's a difference of degrees, but enough to give it the edge for me.
In terms of fixed equipment, I think we're all mainly circling around the Owens and its 3.5 tons of electronics. The Hauptmann, in terms of fixed equipment, kind of falls off the radar since it's not weapons or electronics, it's a freezer in the engine and CASE. Filling your engine with freezers is rarely a bad idea. CASE is also not a bad idea in a lot of cases since, like the Avatar's lasers, it's probably going to wind up on a lot of configurations anyway.
Amen. Any unneccesary fixed equipment is a negative on an Omni, but the Hauptmann is among the least offensive designs in this fashion that exists in CBT. As you said, a DHS that takes up no crits is never a problem, and CASE is handy in most designs, even if it's a wasted half ton on the occasional flashbulb.
The Firestarter. No one would see it coming.
Not even your own pilots :D