Dreadnoks once upon a time, but IG's would be the choice of mine from your list of available choices. You can kind of co-mingle old sculpt and new sculpt together and even though the new ones are REALLY tall they can walk alongside of vehicles nicely.

I kind of used IG's like shadow guards before they existed... Elite troopers loaned out from Destro to Cobra Commander, in case his regular personnel could not be trusted. Also they were excellent when CC needed to purge out any treachery from his ranks... Kinda nice to have "consultants" do that kind of work...