I will tackle the issues seperately, since it seems like everyone here is basically stating what they are willing to "compromise" with one set or the other (i.e..."So-and-So may have better G1 accuracy but less posability, etc.)
SCALE:
TFC Herc, hands down. I see alot of people here talking about wanting "proper scale"..but what they really mean is they want "even scaling" among all of their toy figures. Now, when I say "proper scale", I mean proper in accordance with how they appeared in S1/S2/Movie. Gestalts should TOWER over other individual bots, and although I know it is ridiculous to expect a Devy toy that can actually pick up Henkei Prime in a single fist, Herc comes the closest to that of any of them. HP coming up to Herc's waistplate? Epic. Henkei Prime coming up to FP Bruty's shoulders? Not so much. (NOTE: this is NOT a diss on FP, as I realize it was just a set of add-ons to a failed Hasbron't figure..which I own and love, thanks to FP)
Individual bot asthetics:
So far, with only a few 3P with actual models out (I wont trust renderforms or teaser images enough to give the other companies a vote here), I have to go with FP Bruticus. Maketoys bots just seemed to...Emo-ish (for lack of a better term) to me, and I didnt like how the vehicle parts didnt mesh into robot mode very "G1-like" with TFC's Herc bots...Mixmaster's barrel, scavenger's scoop, and Hook's crane arm all included.
I will say, however, that their take on the aerialbots are looking alot better, but like I said I wont trust teasers until I see it in plastic.
Individual alt modes:
Here I have to go with TFC, once again. Their constructicon vehicles are totally awesome...from the posability of scavenger's scoop to Hook's crane arm (i know we've all added our strings, right?

). Yeah, Mixmaster's barrel doesnt actually rotate, but I am working on figuring a fix for that with my dremel.
Bruticus' alt modes were kinda lacking...from Swindle being smaller than Jazz (seriously...a hummer versus a porsche?) to the totally weak-sauce helicopter Vortex.
GESTALT modes:
Here I have to go with Maketoys Giant. It is the only one of the 3P'ers that came close standing on it's own. FP Bruty being of course an add-on set to save the worthless effort of Hasbron't, and even Herc, mighty as he was, needed a second "Rage" add-on to avoid being too "neo".
That being said, FP's add-on for Bruty was totally awesome. Accurate head, back cannons, sweet weapons, et al. The actual points of failure here I ascribe completely to Hasbron't, and no fault of FP who put out an awesome product to fix what they could with the set.
Kibble:
This is the one issue with which I see no all-around winner. Herc, as he came, was acceptable, but to make him complete (IMHO, to be as G1 as a true Devy needs to be) you had to get the Rage set, which of course does not incorporate easily with the original bots. Maketoys did a lot better with their "tow-along generator forearms", but there was always the "devy head sticks out" issue. FP, although they tried, bless their hearts, to actually incorporate all the upgrade pieces as pseudo-weapons, didnt totally hit the mark either.
And now, if forum rumors are to be believed, TFC is making some kind of "6th-bot parts former" for Uranus just to incorporate Supe's chest plate, and I wont even mention the horrible Energon-Hands of the original Superion and Bruticus Maximus (well, guess I just did).
I could only shudder to think how one of these companies would handle, say, Menasor...remember how his legs where actually formed out of blocky, rectangular kibble pieces and the cars just kind of "stuck" to the fronts of them? Dunno how or what those things would be used as in part of the actual toy set.
I guess the only thing we can hope for is a continuation of the current trend...for most of the 3P-ers to keep competing with each other by releasing similar sets (aka Herc and Giant), and for us to choose what we like best between them...although this will mean a longer time span before we can get ALL the combiner teams we want if each company were to do different sets.