It depends on how you like to play. Rank 20-4, you just need good weapons that deal damage. However, this does not work beyond rank 3 and on. I'm sure you noticed. i suggest you focus on one type of mech and upgrade it.
if you have alot of regeneration, heat mechs and energy mechs are a good choice. I think the best build to getting rank 1 is a physical mech used by nic a long time ago. The "Nic" uses a sniper rifle/Anti-Material (Either one works) top weapon, 1x Demolisher mk3, 1x Caseus/YellowBeam, 1x Antares, 1x Galaxus A and 1x Cannon Feet. Modules are dependent on type of mechs you will face. The most Robust build uses... 2x regeneration modules, 1x Resistance module, 2x Bullet Packs, 1x Hp Module. You can opt for more HP modules or utility modules such as Grappling Hook, teleport, Shield. If you use a shield, I recommend 15% energy/heat.

Mythical Weapon/Parts can easily replace some of the weapons the "nic" uses.

Needle Blaster>Demolisher MK3(Can direcly replace as they weight the same)
Wipeout>Top weapon(You will likely have to put sacrifice some more weight)
Mythical Bullet packs are esssential as they offer more bullets for the same weight as the Bullet storage Packs.
If you want to put distance between you and enemy,
Saurus Rifle>Beam/Caseus

If you face more Heat mechs
1x Heat module 1x Regen Modules>2xRegen Modules


If you face Heavy kit user
Kinetic pointer>Antares

If you face another physical mech
Consider a 15% shield+ more HP

Get better fusions..U have some good weapons for ur mech