I'm pretty variable. My preference is for standard-sized hex bases with a squads' worth of troopers on it. For motorized infantry, I'll put a handful of bike/ATV troopers on a base and call it good. I also like to pop MWDA infantry stands off of their dials and mount those on a base.
For battle armor, my preference is also a squad of troopers on a standard base.
For BA that are too large for this to be practical(basically, anything Phalanx-sized or bigger), I'll make my own hex bases out of styrene sheet(about 3/4 the size of a normal base) and out a single trooper on it. I'll do the same thing with mechanized infantry, placing a single mini of whatever I'm using for their abstract APCs on a small base.
In all cases, not matter how many figures are on a base, a single base represents a full infantry platoon or BA squad.