Well, I think I don't have a preferance based on region as there are designs I like and ones that I loathe from all of the major schools of thought. In general I will say that western mecha tends to be the must plausible and functional seeming. While the Japanese are further along in real world robotics development, when it comes to their fantasy and science fiction most of it comes accross as being TOO fantasy based and impractical, even when they are trying to be "realistic" about things. The now-ancient "Project A-Ko" even made a joke about how with Japanese mech designs there has been a big problem with "where does the pilot actually go" that isn't always obviously addressed even when they show the cockpits open given that there can be subtle angles used to deal with logistical problems between "hangar" and "action" scenes which are pretty obvious, not to mention questions like range of vision. For example in Gundam when you have these things flying through space, they imply the pilots are somehow doing this by eyeballing things through cameras or viewports, when really that's not all that practical given the perspective and what is liable to happen to a lot of those cameras (not to mention the horrible, pitch blackness of space). Sensors are an answer, but "how" isn't even addressed in a science fiction sense, not to mention the issue of stealth technology and so on (if everyone is using cameras, or energy wavelengths to spot each other... like on a submarine or whatever... which brings up questions about the whole fight dynamic which would become more cat and mouse like rather than what we see).
For the most part European or North American mecha designs tend to be far more reasonably presented in terms of their capabilities and what they would be like in combat.
Of course I will also point out that you see less European and North American mecha because while robotics might be great for a lot of things, manned humanoid combat machines are not one of them. Basically if you've got the technology to make a manned robot that can walk or fly, you have the technology to make a tank that can do the same thing. All of the space used to make those arms and legs and such move in a humanlike format can be used for more speed, armor, and firepower. Heck if you need to you can put little EVA arms that fold out of a panel or something for hostile enviroment work.
I tend to feel that mecha are cute/cool, but a sign of fantasy similar to a wizard wiggling his fingers and throwing fireballs, in most cases I can't even consider it science fiction even when it's trying to be because the basic idea is so ridiculous. Legs are one of the stupidest ways to move a machine of mass destruction. I believe the future would be more about all enviroment war pods (basically tanks) than anything if it comes to that.
As much fun as it is to show a giant robot stepping on current sized tanks and such, most fiction overlook what would happen if say the tank was the same size as the robot. Truthfully given the differance in optimization I don't even think it would wind up being much of a fight.