First let me give you some idea of teh diffences between mech, emch and zoids.

Mech, an american idea (Some say it cam partial from japanese mech but who know for sure) are huge Leged tanks. Mechs never truly look like anything even the spider mechs don't look anything like real spiders. Both mecha and mech are based on the same idea, mobile unit with the power of tanks but the mobility of troops. The ablity to traverse trick tarren with easy.   The difference is that Mech tend to look like tanks with legs. Their blocky and look unjainliy but because of andvanced leg controls and Gyrow are stay standing under even the most heavy attacks. Mecha are different, they tend to be design with looks in mind. Most tend to look like suits of Armor. Many are actual built along that idea. What seperates them is the American and Japanese mind set. We american wnat things to jsut work while the Japanese infuse thiers with art. In the end nether is better or worse. Mech may not always look good but the sher fire power they can carry starger the mind. Mecha tend to be light in desgn, desing for close combat (limited long range cablity, fast combat (long range fire with high speed but normal low calaber weapons.) and very slow heavy combat. They tend to carry fewer weapon and are smaller in design. the heavy combat models tend to me very slow and easy targets. Mech are sure giants. And don't let their mere wait of 100 tons fool you. Mech are design with extremly light materials. But these Materials can brush off laser and cannon fire like it rain drops. The heavy mechs tend to be giant that only a another heavy mech or special modifed/armed mech can take down. Laser swords like those carried by many Mecha would have no effect on them, their armor holding up agaisnt quite will. Only heavy weapons like Beam cannon, Buster rifles, and heavy Cannons would be any effect. In this case a mech facing a mecha with these weapons would be equal matched. It would take severail shots from there weaposn before a mech would be heavly damaged and the mech while big are not slow and if equip with jump jet would be hard to hit. If both units have skilled pilots then the battle would be a long one most likly ednign in both units distruction.

On the other hand mecha would be hard to hit by a Mech because it sher speed except by the most skill mech pilot or pilots using Targeting Computers and a Artemis IV Control System.  The targeting can predict the ecsact location even the fastest mech (over 93 mph  or over 150 kph) and mech designs and tell you where to fire to hit them. A good pilot with this system rarely misses. It as allow a pilot to hit a specific area. Such as head, legs, arms, chest, shoulder and so on. The Artemis system allows missles to lock on much quick and be more accurit. While it's rare for all of a mecha missles to all hit this is not the case with mechs. Do to their sher weight and cost every missle is a prized postion. Mech missles are design to carry emminse loads of fire power with a fair small size (yah right their still huge) and be deadly accurt. I've only seen them miss when agaisnt one of the smallest  mech who had MASC system installed and the fire mech didn't have a targeting comptuer isntalled or a Artemis system install. It normal trageting comptuer couldn't predict the smaller mechs movement. course the samller mech was still waste ebcasue the pilot if teh larger mech new how to compensate for fast moving targets. For those that don't know it the MASC is a system that boosts a mech speed but cause it's engines to over heat. the speed difference whenit off and on are large. Some smaller mech get a  20-30 kph boost. But only the larger mechs cna handle the heat build up continusly. While mecha can be many tiem faster then a mecha that speed not going to help much. Only mecha like gundams could stand such a attack but not even their Gundaium could stand it for long.

Then we factor in Autocannons, Lb-x Autocannon and Ultra Autocannon, Gauss rifles and PPC. All of thesem while the first 4 are weaposn that fire ammo, would devastate a mecha. I've seen a brasha of Autocannon fire take down even the heavyest mechs in one shot. Same the the gauss cannon. But like buster rifles/beam cannon carry by unit like the mecha Wing Zero (5 shot of it weapon at full power is what I hear) they have a limited amount of ammo. And like the buster rifle they can be dodged quite easyly if you know what your doing. PPC are another matter. As long as a mech doesn't over heat it can be fire non stop because mech their own internal fusion power plant. Just don't be near one when it over heats. They explore like neucler bombs.

Zoids area another matter all together. They tend to be a mix of both mechs and Mecha. Huge mechians that can large amount of armor, weapons, and good speed even on the heavy one. Their armor just isn't up to mech or Mecha standards though. For a good reason to. Zoids tend not to be weapons of war, unlike mechs and mecha. With Zoids your not trying to kill both the pilot and unit like with mechs and mecha. Thier weapons tend to be of lesser strenght to. their amin dueling units, design for people to test their comabt skill agsint eahc other and survive to fight again. Much like sword duels where no killing is allowed. But I don't know all the rule of combat. Even groups like the Backdraft group tend not to kill the enemy pilots.