Hi.
SL has been here for 20 months now, but I don't remember ever seeing a good thread about end-game symbiants. I'm just done with twinking on my symbiants at level 220, so here's my list.
A small note: Yes, traders can equip QL 300 symbiants, but only in R-wrist and left-wrist and left-hand slots. You don't even need Burden or Gemini for R-wrist, but it's 40+ perks that you have to have. You also need 2x of the 3972 Chapman pistols with +25 treatment each. 290 is equipable in most slots and 280 head is possible, but you should have burden + blue belt of Maar for 280 head. The hardest slot to equip a high QL symbiant in, is chest. (atleast for Opifex.). loosing the Stamina buf when equipping hurts alot.
All my choises can be found in my signature. Just note that Eye is wrong since Auno hasn't added Extermination Eye to the list.
Head
Control if you do tradeskills or are using Chemical Blindness, else whatever Control or Support you can get your hands on. Artillery got RangedInit, but it's not worth loosing all the abilities + NanoCInit and NanoResist for that.
Ocular/eye
Probably the hardest choise of them all. Artillery got AimedShot, but you loose tradeskills(Chemistry) and important abilities stuff. Control got the abilities and everything else you need except that very Important Aimed Shot (if you pvp) Extermination Ocular is also a very good alternative but you'll loose out on nanoskill.
I ended up with a QL 240 Extermination Ocular.
Ear
The only option to Control Ear is the Support Ear. Artillery is junk. Until level 220, most people prefer a Ql200 Implant with 7% XP.
Right arm
Artillery all the way. The only problem is lack of burst. Since getting higher QL than 220 is extremly hard, hotswapping with ql250+ burst implant for equipping Burst weapons is very easy. Control+ Support got AddAllDef, but I don't think loosing shiny shotgun is worth the extra defence.
Chest
SMG users want to use Artillery. As pure shotgun user, I went for Control symbiant. HP/Bodydev+ abilities = Teh Win.
Left arm
Close between Control and Support. Install the control if you have a choise, but use the highest QL of any of those two you have.
Right Wrist
Artillery is the only viable option here. Pure shotgun users might think about control, but loosing 130 RangedInit is bad both in Solo and PvP.
Waist
Another hard chose between artillery and control. Control got better defensive values, but lack the Shotgun buf that artillery has. I landed on Control because of bodydev, NanoCost, Nanopool and sense.
Left wrist
Everything is junk. Install an Implant with NR, Runspeed and AddDam.
Right hand
Artillery here too, as everything on right-hand side of the body. You'll miss some faded tradeskills but gain every weaponskill you need.
Thigh/legs
Again, control got all the defensive stuff. It also got all the abilities for nice trickle-down and a nice healdelta. Artillery is not a bad option if you can't get hold on control. Support lacks the defensive stuff, stay away.
left hand
I started out with Artillery, but I now think Control and Support is better with NanoRange and Interruptmodifier. The only difference between Control and Support is the AC. Get the highest in any of those two. Those into RangedEnergy should stay with Artillery
Feet
Control is the only one that got all the defensive bufs and abilities and it got heal/nanodelta. Artillery is very disappointing in this location since it lacks AddAllDef. Support is junk