If we talk about strongest players we need to make a clear distinction between old Gen and new gen. The old Gen did pioneer work but the game was far less complex. The new gen had the advantage of building on the work of the old guard but made the most out of all the new possibilities.
So I will start with the old gen:
1.) Toru: Most of you will not know him but whoever plays stun lock walks in the shadows of Toru who made the first > 95 % win rate team. I think somewhere on YouTube there are still videos of him. He destroyed other top 10 players with absolute ease. In the first year of the game he was considered some kind of Demi god.
2.) Hidan aka GGMadara: Uncompared to this day in terms of decision making. Inventor of several completely broken strategies and the guy who forced the devs to implement proper testing before releasing new stuff.
3.) NMA Alucard: Hidans Twin in mind. What hidan was for decision making, alucard was in terms of teambuilding. Completely dominated everyone for two seasons with AegisBlade, then - when nerfed - followed up straight with ZibGazer (together with Hidan). Didn’t have the temper of Hidan so often overlooked.
4.) Tyrone: Famously known for misspelling monsters (zibarius), Tyrone was the first CEO of Frontlines, Nightrider, Zibkong and Frost + Soul were one of his most famous and soon to become all time classics. Probably the guy who got the most FL combos nerfed.
5.) Pro! later known as Kei: Longest period of dominance in this game before mister X arrived. Kei was a frontrunner par excellence. He won with the first half of his, then brought his advantage over the finish line.
Honorable mentions at this point to Saul, Tjaine, Michael N, LightGM, Buck and Zard.
New Gen:
It’s tough to choose but with a bit of bias the first to mention here is @Unown. He was so good that “See, I beat Z19 Ante - see, nobody cares” became the forums most famous meme for a time. Great Guy, Great mind and probably the best mid game player of all time. He’s like a spider happily letting you walk right into a trap, patiently waiting for his prey .
2.) Credit where Credit is due: Mister X. The most dominant person of the modern Era. Most top1s, longest win streaks, highest WR with more than 50 matches played (100 % lol) and the guy who made the most annoying strategy ever famous: AP Spam.
3.) Josu: Sacrificied more number 1s for personal dignity. Like a Samurai took pride in the attitude to rather not get first with a strat than to go with the masses. Made Motor famous again when everybody said he’s dead, made Void look absolutely broken, invented Haze. Also a great guy. I think I’m in 1:27 against him in ranked PvP yet there’s one match between us on his YT channel: His loss against me. That tells you a lot.
4.) 
No words needed: The man, the myth, the legend. Nobody got top 10 that often never using the same team twice. Nobody is this creative and Lemmy is without a doubt the nicest guy I never met. It’s ridiculous. Any list without him is severely flawed.
5.) Now it’s getting tough but I‘m gonna pick @NMEGaryOak here: Gary is often overlooked but I admire his attitude of building a team like a master craftsman. In a Time where everybody jumps the bandwagon of the newest meta ■■■■, Gary since countless seasons works on perfecting one team. He has targeted specific myths for a specific spot in this team. Every monster serves a purpose. If I had to name my favorite team ever, it would be Gary’s rock lock team.
A few honorable mentions here as well:
- Ducky for his dedication and improvement over time in PvP. Amazing at analysing teams. Would have made the list if he wouldn’t have jumped literally every meta bandwagon.
- Dracarys: An F2P genius. Made my favorite Cani Teams.
@GMagic: Facing his teams is like running into a brick wall
KD: Suffers from PvP not being PvE but is a prime example of how strategy can beat pure fire power. Also built the most successful OoO up to this date.
That’s it for now 
Someday one of us needs to get 1st with OoO, so it can have a proper mark on the history of the game!
Been curious since then and who created those famous FLs