Max endurance would be full fl set. IDK what the best sets are. I asked this question earlier and here was the answer giving credit to RaYZER0X
For max dmg:
Helmet:Gold(-16 armor, +200 ranged dmg)
Platebody:Spectral Vanguard Platebody(+100 all dmg type, +32 armor)
Platelegs:Spectral Vanguard Platelegs(+100 all dmg type, +25 armor)
Feet:Guardian lower legs(+35 all dmg, +12 armor, 3 walkspeed)
Misc:Brain monocle(+30 Ranged dmg)
Back:Ranger's Backpack(+40 Ranged dmg)
Ring:Hightower ring(+30 Ranged dmg, +3 armor)
Neck:Tri-Color Necklace(+25 all dmg)
Total stats:
+560 Ranged dmg, +3 walkspeed, +44 armor.
2.For more mobility but less dmg
Helmet:Gold(-16 armor, +200 ranged dmg)
Platebody:Machine rug(+70 ranged dmg, +5% endurance, +38 armor)
Platelegs:Machine rug(+80 ranged dmg, +5% endurance, +30 armor)
Feet:Spider Stilits(+4 armor, 7 walkspeed, +40 jump )
Misc:Front Bullet Pack(+5 Ranged dmg, +50% Ammo return)
Back:Ranger's Backpack(+40 Ranged dmg)
Ring:Hightower ring(+30 Ranged dmg, +3 armor)
Neck:Tri-Color Necklace(+25 all dmg)
Total stats:
+450 Ranged dmg, +7 walkspeed, +67 armor, +40 Jump Power, +10% Endurance.
3.For fully ammo return and mobility
Helmet:Drillbit Head(+16 armor, 75 Ranged, +20% Ammo Return, 3.5% Endurance)
Platebody:Drillbit Chassis(+38 armor+75 Ranged, +20% Ammo Return, 3.5% Endurance)
Platelegs:Drillbit Legs(+30 armor+75 Ranged, +20% Ammo Return, 3.5% Endurance)
Feet:Spider Stilits(+4 armor, 7 walkspeed, +40 jump )
Misc:Front Bullet Pack(+5 Ranged dmg, +50% Ammo return)
Back:Ranger's Backpack(+40 Ranged dmg)
Ring:Hightower ring(+30 Ranged dmg, +3 armor)
Neck:Tri-Color Necklace(+25 all dmg)
Total stats:
+325 Ranged dmg, +87 defense, +10.5% endurance, 100% ammo return