Since I have not been playing for long, this information might not be too helpful, but I'll try my best.
The best decks in format right now are Yveltal EX / Darkrai EX, Aromatisse XY decks, Plasma (Lugia EX or Kyurem PLF), Virizion EX / Genesect EX, Blastoise / Keldeo EX / Black Kyurem EX, and Emboar / Rayquaza EX. However the current format also has a lot of variety! You can many decks (ranging from rogue to tier 1) at the
deck garage forum.
Besides that, durant is out of format as of last years rotation. Sorry.
Not sure what you mean by chandelure. All of the chandelures are still in format (the oldest one is only in thanks to a secret rare reprint, but the original print will still pass). That said, none of them are all that competitively viable.
NVI chandelure's ability is weak since 3 damage counters doesn't mean much considering how difficult it is to get them. It's generally outclassed by muscle band XY, silver bangle PLB, and Hypnotoxic Laser + Virbank City Gym PLS. ND chandelure isn't strong enough for a stage 2 (this is a fast format), and PLF chandelure is largely outclassed by Emboar. .
Unfortunately, there are not any really viable mill decks in format, like durant. The best card we have is Malamar XY (with mental trash) which combos well with red card XY. People have made decks for this, but they're not going to compete with the top tier decks. If you're into control decks, though, then Trevenant XY / Accelgor DEX is quite strong (though loses, generally, to decks using Virizion EX, which blocks special conditions).
Most of the tier 1 decks right now are fairly straigthforward, do-lots-of-damage kinds of decks. Besides that, there are some strong decks utilizing non-EX attackers right now, like Flareon PLF / Raichu XY, and Empoleon DEX floating around.
tl;dr the format right now is fast, but there's a lot of options to choose from. Have fun!
