This might be "I only have this one right now" bias, but Lowb is def the coolest one of the 3 for me (design-wise), and its sounds are pretty intricate.
I haven't gotten a good listen to the other primordials, but I wish the MH would've carried over the "lots of different sounds that work really well together" part from Lowb to the others. I get that having a lot of instruments for 5 different monsters each would be overkill, but Lowb set a precedent that the others just didn't follow imo