What is your favorite team comp?

Lmao I thought you were talking about league team comps

Predator with steel and/or crystal+poison with the predators stacking ionic sparks and thornmails. Preferably WW with the ionic sparks and Skarner with thornmails.

Poison makes ionic spark do extra dmg, ionic spark AoE can proc predators execute. Extra AP on WW makes him do more dmg, so he heals and survives longer. If he executes someone during his ult, he heals the execute dmg as well.

Great comp into ocean and mages. Gets countered normally by lights, sometimes rangers.

Position yourself well to make the most out of the ionic sparks and thornmails.

If you can't get predators, try the ionic sparks on warden x mystic or light (ionic sparks preferably on Nasus)

Main idea is to keep the ionic sparks on members that last on the field forever and let the enemies kill themselves.

Been having fun with Glacials/Poison recently. It sounds a wierd combo but mundo is the best extra berserker that volibear and olaf need, twitch gives ranger with EZ and freezing gives extra time for Singed to spread his poison

endgame:

4 crystal + 2 ranger + 4 warden + 2 luna + 2mystic + (2 glacial or 2 ocean)

Frontline: Taric, Braum, Leona, nasus / amumu

Middle: Karma, Janna

Backline: Lux, Ashe, Ezreal

getting the right items is the hardest part. If the game throws and at you instead of and you are screwed and have to play something else.

3 Electric, 2 Lunar, 2 Rangers, 2 Glacial, 2 Warden, 2 Mystic/Crystal

Depending on the current patch, something that's not meta (i.e. you don't get a lot of competition for your champs) but counters most of the meta comps.

At least 2 Wardens and 2 Mystics, and then a couple more depending on what the opponents are building. Like, if you see somebody building Deserts then there is no point in adding any more Wardens. And if there are no strong Mages, Inferno or Posion then you don't need any more Mystics.

Then add a strong ADC, something that has a good synergy with whatever Wardens and Mystics you manage to get (examples: Yasuo + Janna, Ezreal + Braum, Jax/Aatrox + Nasus + Soraka). Or something that's good at countering your opponents (ex: Kha'Zix is great against the Shadow meta, he clears Malzahar summons fast).

Items are more RNG dependent. Good defensive stuff for your wardens or good offensive stuff for your ADC. Just don't sit on them, build something as soon as you can.

Lulu is God - Set 1. (Because this wasn't really a synergy thing.)

Stack Lulu with as much AS as possible (Rage blade was a must), Tears also workable. Build comp with the express purpose of keeping her alive (Guardians were high value picks). Once rage-blade got going, she'd chain stun/heal the match into oblivion. Just had to be careful of the timer. "Lost" far too many matches because neither team was dead yet before the forced quit timer ran out.

Dumbest and most hilarious off-meta comp that I could consistently make work.