Buy a stalker and put Missile Racks 6 on it. That's a very deadly pair.

Get Guardian, it's considered by most players to be the best Rare mech, good enough too even compete against Legendary mechs.

it depends on what weapons you plan on using, could you tell us that first? because the type of mech to use depends also a lot on your play style and what you're planing on using as the main weapons. 

@Peulut What's your in-game username?

get stalker rank it up and put dl8s on it

Tengu is realy good and can effectively counter most mech and if timed properly you can dodge the Zepher ability. But it requires a LOT of skill to use

(Most people don't know how to use it very well)

Tengu used to be great but now it is obsolete becaue of the grade update and will become unusable when you reach 3000 sp.

Stalker with disrupter 16 is a my go to. 

But what If they're free to play? You can't get disruptor 16 through anything but the ecr, and it's gone already.

Stalker Arc Torrent, RAW DPS, put Missile Rack 6 on Ares. Worried about health, it can just heal.