My personal thought is the more variety the better. HT/Mazuri is a balanced general rodent block - hence the term "base diet". IMO HHB is more like a necessary "supplement" b/c it contains the extra calcium to prevent MBD and is formulated specifically for squirrels. Plus at $17 / bag HHB Adult would cost me well over $100 / week if thats all I fed my crew of 8 (soon to be 9 with the paralyzed boy from dextersmom). I call Teklad my main or base diet b/c it's always available for them to nibble and they get one HHB adult in the AM and one in the PM.
I don't know that there is a textbook diet for a squirrel. No squirrel is going to lack nutrition b/c of eating just HHB or Teklad as the only block. Like Astra said block is necessary and I agree. I just choose to do Teklad and HHB together to round the diet off as much as possible and HHB x 2 is absolutely necessary. IMO there is no better formulated food for squirrel's than Henry's. I have mentioned to Leigh doing a finer grind on the Pecans so the flavor is disbursed better throughout the block so they don't pick the block apart looking for the larger pieces.
All are good choices - a bad choice is a block containing timothy or alfalfa (Nut Squares come to mind). For Prairie Dogs dried corn is poison as it destroys their gall bladder. My Prairie Dog only eats Brisky PD Pellets and free choice Timothy. In his case Timothy is the actual base diet (on demand) and the pellets are the supplement. Although he is a true ground squirrel his diet is way different from his tree dwelling cousins.
Patches says Hi!