Level 6 Synchro

I think that anyone noticed that, LV6 Synchros actually left aren't that good. The moment Brionac was banned, synchros lost the little playability they still had, why's that? Brionac is one of the best synchros level 6 is easily accessible and the effect was really versatile and not limited to once per turn. Little cost that could be abused to clean for OTKs or looping (just think of all the Infernity Loops or Fableds, or random FTKs, and so on). However, Brionac was the first and usually sole synchro option when going for LV6, because other weren't even a quarter of Brio's power. Still, Brio was banned, and we lost our LV6 synchro option, effectively killing lots of comboes or power-plays, may it be synchro climb or just a random synchro to draw with Librarian's effect. People almost instantly decided either to totally drop the synchro part in their deck to focus on XYZ sheningans (or main deck ones, like BLS and such) or to find a substitute for brionac. The main choices were Iron Chain Dragon and Gaia Knight, the Force of the Earth. Let's analyze them:

1 Tuner + 1 or more non-Tuner monsters You can remove from play all "Iron Chain" monsters from your Graveyard to have this card gain 200 ATK for each card removed, until the End Phase. When this card inflicts Battle Damage to your opponent, send the top 3 cards of your opponent's Deck to the Graveyard.

Well, why do some people choose this over gaia? Because of the milling effect. Still, I totally find this unuseful, if not dangerous for yourself: setting-up your opponent's grave isn't a good thing for the 80% of the deck in this meta. 2500 ATK is good, but gaia's 2600 are better, since he doesn't need to sucide against stardust, shi en and others.
To be blunt, then, I totally don't like this card, and I (I, ME, that's personal, you could particularly like this card for some unknown reasons, and, if you do, it is unuseful to talk, since you're probably so convinced that nothing would change your mind) won't recommend anyone to play this card over Gaia.

Let's see him, now.

1 Tuner + 1 or more non-Tuner monsters

Well, no effect. Actually, this card is better than Iron Chain, in my opinion. 2600 ATK, better than Iron Chain's 2500. No milling effect, thus no risks in attacking your opponent to deal some damages, but, what's more, there's no effect at all. The awesome thing about this part is that Fiendish Chain doesn't do a thing against this, and, even though this one is really improbable to happen, your opponent can't randomly veiler this card just to have a random LIGHT monster in the grave for BLS. Good card, if I were to choose between one of those, I would, without any further thinking, choose this one. HOWEVER, there's one more thing I want you to see. There's a synchro option that only few players consider, and just a little part of those plays:

1 Tuner + 1 or more non-Tuner monsters During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent. This card gains 300 ATK each time it inflicts Battle Damage to your opponent.

So, what about this card? He's the thing I wrote this post for. I like this card over both Gaia and Iron Chain because of the piercing effect. Everyone in here hates, at least a bit, Reaper, right? Well, Reaper hates this card. Why having a card that deals constantly damage to the opponent while building-up its strenght shouldn't be considered for competitive plays? This runs over spy, while dealing damages, or even over recruiter. This runs over Mother Grizzly (yeah, lol), while dealing damages. However, the main reason is that this card by itself totally defeats the purpose of setting a monster to avoid battle damages, and that's great. After little time, if protected and well-played, this card can even be better than gorz when he's summoned after the opponent's deck's boss' attack.

Overall, Gaia should be used, Uruquizas too. If you have one slot, play the one that would be better in your meta (gaia is good against decks like rabbit, six and others that have some monsters under 2500 ATK, uruquizas is good against, strangely, Inzektor, some wind-up situations, reaper, and cards like Maestroke, eventually GK, sometimes GB), I usually like uruquizas better (on DN), but depends on my deck and if it plays easily summonable beatsticks over 2500 ATK. If you have two slots, don't hesitate to play both.

That's All Folks.