I'd definitely like to hear what others think though.
To put in my 0.02€ ... I think you are on to something.
Right now I prefer the walking poses for two reasons:
- (usually) the part count allows for easy(ish) reposing (if you don't like the walking pose as sculpted)
- only one foot has to be cut off the integrated base (a HUGE advantage)
I don't mind "both feet on the ground" poses if they are not too static. The Warhammer you mentioned is a very good "best practice" example in my opinion. The knees are bend, the stance is opened slightly. The whole miniature has some animation, no matter how you angle the torso. Even the most massive Mech shouldn't be stark and stiff in my opinion. This doesn't make for a very appealing miniature, no matter how good the details are.
A good mix between walking poses (with at least one foot off the base) and action poses, but with both feet (mostly) on the ground sounds desirable to me.