In the realm of fantasy, mechas kick everything's ass. Why not? They're basically 50+ foot tall warriors bristling with guns on every body part, that may or may not have the ability to fly or shapeshift.
In reality, however, the design is pretty absurd. Since its center of gravity is much higher off the ground than a tank's, it could much more easily be tripped over (ever seen
The Empire Strikes Back?
The Battle of Hoth is a perfect example of why a walking combat vehicle is a bad idea.) It also has no treads, and thus will have more difficulty moving over unstable terrain (gravel, sand, mud, et cetera).
In media that features mecha, their main advantage over tanks is that they are larger and have more/stronger weapons. In theory, however, tanks could be made that large and have those same weapons.
Realistically, a mech would be usefull on the battlefield only for the intimidation factor.
Vexar wrote:As far as tanks... We're more likely to see them 'Hopping' along a battlefield in the near future, rather than any sort of mech.
Like a
Mako? I want one.

Okay, so that's more of a rover than a tank, but still....