i have a bunch of 3P figures, but i dont think i have something from everyone. i dont know if i can rank them, but ill give my opinion based on what ive got.
fansproject:
warbot defender, intimidator, explorer/munitioner, city commander, G3 trailer, columpioas one of the "first" 3P companies you can see a definite learning curve, and have even their springer has even been bested hastak. but theyve only gotten better with time. their combiners look phenomenal, but are delicate. stand alone figures however are really solid. even combiner pieces when separate are really solid and inspiring.
igear:
cogz, duneraker, rager, hench, spray, bushwaker, veer, ufogotta say, i love me some minibots. and i love igears renditions. i know theres a lot of criticism over some, but they hit the nail on the head for me. hasbros recent swerve and cosmos did replace my veer and ufo, but it doesnt bother me. those were the weakest igear ones anyways.
KFC:
boxbomber, rhinohorn, ironpaw, MP10 handsthey can be delicate, but i do like their designs. im willing to give them another shot or two as ive heard theyve stepped up their quality.
maketoys:
battle tanker, hyper novae, chaos/paladinso far, solid figures. their new battle tanker "base" figure is borderline KO, but their original designs are inspired. what gets me though with the figures i own, is the price. for what they are i feel theyre overpriced. my next MT piece will be quantron which is pretty spot on for price, so maybe high prices arent a trend.
mastermind creations:
knight morpher commander normal & black versioni know right? thats all i own from MMC? well, their debut piece was pretty good. and the black HOS prime was even nicer. now they werent amazing, but really impressive for a first try. after that, their pieces were too expensive for me at the time. i did want the seekers and shockwave, but that ship has sailed

. their predaking isnt my cup of tea, but im planning on getting a handful of azaleas and the reissue hexatron. so ill see.
perfect effect:
wardena really phenomenal figure. must have companion piece to fort max.
planet x:
caleus i wanted to get genesis, but damn that price tag. their swoop is a really nice figure, but the heel on mine snapped off right out of the box and some pieces of him are sharp like a knife! maybe its just mine though. neither of those things stop him from looking great on my shelf though.
tfc:
hercules, ares (nemean)i love my herc, but he's not as solid as id like. im not sure if that just a consequence of being such a large combiner though. i plan to get the rest of ares, but nemean as stand alone figure is pretty nice. solid robot mode, and nicely proportioned lion mode. ugh.. ares sword though...
toyworld:
grind rod, aurora, hardboneif i have a favorite, its probably toyworld. i dont even know if i can describe why though. maybe its the big clunky aesthetics masked with surprising posability. grind rod might be my most favorite 3P figure in my collection. its just a fun *&$#@ing toy!