SLKR >> Rey > JML > SEE
PvP is close for all of them. They can all win on offense even when facing hard counter without destroying multiple teams (JML might now be worst in that regard). Defensive viability is low for all of them. I would put them all “on par” with each other in regard to PvP. Subjectively, this will vary from person to person or (maybe more importantly) shard to shard.
So then my rankings move to PvE content. SLKR destroys raids, easily the best. Rey does better than JML in CT Rancor and SEE has little raid viability. All of them add TB viability with Rey/Kylo edging JML/SEE on leadership, but Rey/JML are potentially more help as the difficulty of LS is much higher than DS. (JKL is probably the best LS Geo lead.) There is not an assault battle for resistance, so that drops Rey slightly. So ranking this area has SLKR >> Rey > JML > SEE.
If we add in the prerequisites: they all include characters that have little value in terms of usefulness in the game to varying degrees. FO perform relatively well and can easily be used with SLKR (swap in SE/Thrawn vs JML). These are fairly easy requirements, but requires Finalizer (ship development). Resistance can also be used quite efficiently with Rey (swap in powerful Jedi/Rebels for better arena viability). Rey also requires some fleet development for Raddus. JML has some good prerequisites but requires developing your roster for quite some time (GET crunch, legendary toons, relics for JKL reqs). While JML prerequisites include JKL, Hoda and OB; they are more for creating other teams (Mothma, CLS) than bolster his own viability (need JKR, GAS, Basti, Wat for common teams). I find these requirements quite expensive, but mostly useful. SEE’s prerequisite characters have very limited use/viability under SEE lead, but they do start the imperial troopers team. One will need to develop SE, Triumvirate, Wat and Armorer in order to achieve true offensive viability against all teams. SLKR/Rey > JML > SEE imo here.
I think they are all good characters, but I think SEE and JML could use a tweak.