[@Dynamo Frokane]  I would actually suggest that, rather than a progressive tier of straight up best from worst, the mech tiers each have their own advantages and disadvantages.  And in turn, all tiers are available to players, so that they have some technical variety.  

My suggestion would go this way, though feel free to adopt as much or as little as you like:

[hider=Suggestion]

Mk I: Old fuel based systems that run on diesel(or, in some cases, gasoline).  Forms of these mechs have actually been in use for centuries, but most of the ones in use today were made in the last four decades.  

[b]Advantages [/b]

Range and versatility.  A Mk I can be refueled basically anywhere that's even remotely civilized, and so they are a godsend in the Fortune Region, where Elementus is basically inaccessible most of the time, and overhead Solar Orbital Farms(SOFs) are rare.  

Weight and armor:  Mk I's have the highest maximum weight capacity, and can carry a lot of armor, or drag heavy loads.

Cheap: They are inexpensive to build, maintain, and repair.  In fact, many pilots are able to enact temporary fixes on the fly in the middle of a battle.  

[b]Disadvantages [/b]

Speed to weight ratio:  More than the other two generations of mecha, the Mk I's get dragged down by heavy weight.  The heaviest class of Mk I is basically a fortress on legs, but it can't move fast enough to keep up with a modern battlefield.  

Fuel:  Though their fuel is universally accessible, it takes up a lot of room and doesn't stretch as far.  A Mk I uses a lot of its precious weight ratio on gallons upon gallons of fuel, and a long battle could force them to retreat for refuel.   

Heat and Burn Out: The subsequent generations don't have a need for an extensive cooling system like the Mk I's.  A pilot has to watch their heat, if it gets too hot, it can cause permanent damage to some parts, and could even ignite the fuel tank and cause a complete burn out.  


~~~


Mk II: Built using advances in battery and generator technology, the Mk II's replace piston and gear driven joints with servos.  They are able to more closely emulate organic forms, to make machines that appear humanoid, or mimic animals.  The best ones use both an internal battery, and a generator of some form, nuclear being popular.  

[b]Advantages[/b]

Stability: Cooling is rarely an issue, and even the nuclear based generators are stable and well shielded enough not to be an issue.  


[b]Disadvantages[/b]

Refueling: Most don't have a generator powerful enough to keep all of their functions running, and need to have their batteries recharged periodically.  Most have enough power to last between 48 and 72 hours of continuous use(varying depending on exact specs and how they are used).  This is still a strict upgrade over the old Mk I's, as long as an adequate power supply can be found.

~~~

Mk III:

[b]Advantages[/b]

Refueling: An Elementus Core is, for all intents and purposes, unlimited.  In theory, it will be drained dry eventually, but to date not a single Mk III has ever needed to replace its power supply.  

Power: The new power cores have a much greater output than the previous generations, giving Mk III's a great upgrade to the outer limits of their speed and agility.  

[b]Disadvantages[/b]

Repair: Mk III's are the most complex generation of mecha, and can't be repaired or maintained by just anyone.  Whereas no Mk III has ever run out of power, many have been retired simply because of wear and tear on their auxiliary systems.  
[/hider]

I'll finish this write up later, if you decide you want to adopt the idea.