There are a few things that affect an item
-Item level, which goes from 1-5
-rarity, which starts at common (white) then better (green), artisan (blue), epic (purple) and priceless (gold)
-Quality, which is given as a range when you loot the item, once looked at in sell parts screen/hangar you can see the final roll, higher is better
However, the part you want to use is the part that lets you make the servo play the way you want. Bigger numbers are meaningless if you don't use that number on that servo 
You want a servo team that compliment eachother, this can be done in various ways, there isn't really a meta best build so far in beta 3, and there may not be at this point because part variety is getting real good.
For example my current trio in coop is:
2x assasin rifle champs with frag grenade/ammo box combo on shoulders, ranger ruckus modules in cpus, swap out assasin rifles for wide shot rifles for more aoe over less burst, piloted by Reese and Hauk
1x hybrid tank/anti armour drill champ, armour plates on shoulders, highest armour legs and torso I got, dual epic or priceless loader drills with trample, piloted by blink. could replace this with officer pistols if you don't have trample drills but officer pistols are rarer lol. also has soldier firmware 2.0 in both cpu slots
Reese leads, Blink 2nd, Hauk 3rd.
The tank runs out first, mitigates up to 90 damage a hit and does a bunch of trample damage, the other 2 fire off grenades, snipes, orbital strikes and use pet to control problem creeps. When the tank gets low it can teleport away to a beacon/dropship. good damage mitigation, great single target dps and mediocre aoe damage. swapping out the rifles for wide shot ones improves the aoe at the expense of single target DPS but makes it a little more rounded. I then either back them up with soldier drones with building damage tech or behemoths with aoe tech to improve performance against lots of small targets and buildings
I have another variation on that theme for PVP, this is just 1 build though, there are many, and we don't even know all the good ones yet. Try come up with something cool with the parts you have and don't be afraid to try something new.