Got a slight preference for japanese mecha because of their weaknesses they make fight a little bit more interesting.
Sure they would hardly hold against a good LRM20 volley, but hey most battletech stuff was ripped of Macross/Robotech for what I know ( this is less true now after the lawsuit they got up their asses).
However I grew as a fan of mecha, beginning seeing the AT-AT/AT-ST from star wars movies, then going on playing mechwarrior 2/3 and watching japanese mecha/robots on television most of the time (I also played steel battalion, but mechwarrior 2 still keep my heart, oh and I pretty much like the virtual on series ).
Sure japanese mecha design are cool, but that's mostly design, I would say it would be very impractical for storage/maintenance (plus hours of paint job to keep the cool aspect ), on the other hand most of western mecha fill their goal in giving a somewhat more realistic approach as seeming easier to maintain, can use extra part from other design, and still remain somewhat cool enough regardless the paint job, and give them the realistic firepower they could handle (where most of the japanese mecha rely on hidden trap, teleported gun to give them more firepower).
But again in fight japanese mecha tend to be more interesting (lousy aming/gunpower, more close combat ) , whereas most western mecha would snipe themselves to death.
PS : Love the mechwarrior 2's intro, including "the clans","ghost bear legacy" & "mercenaries"
PS2 : As we also consider power armor in the "mecha definition", my first power armor for me was the Iron man