First off, where's the rest of your team? I need more information if I want to compare the two. Other than that, I'm going to pretend that you're just going to pick between the two as the starter/head of making your team.
First, let's start off by looking at Charizard, more importantly, Mega Charizard X.
Ability: Blaze (HA: Solar Power)
Sp. Atk: 109
Sp. Def: 85
Mega Charizard (X)
Ability: Tough Claws
Sp. Atk: 130
Sp. Def: 85
We know that Mega Charizard is more of an attacker, rather than a mixed one. Looking at stats, Mega Char X just gets buffs in attack, defense, and special attack from a regular Charizard. It's not really a hit-off with stats.
I think we may need to make small changes to Mega Char X's Moveset. Here's what I have in mind of what you could use:
Flare Blitz (risky)
Dragon Tail (not really recommended)
Power-Up Punch (not really recommended)
Giga Impact (risky & not really recommended)
Lastly, let's split up the EVs if you're going to use him:
Sp. Def: 55
See how I mainly spread it to the Atk. and Spd. (because that's what I think Mega Char X needs a buff at) and also minorly spread it to Def. and Sp. Def.? (You want to might think carefully about who and what's hitting at it, so adding the small buff is good enough.)
Now let's look at Chandelure.
Ability: Flame Body/Flash Fire (HA: Infiltrator)
Sp. Atk: 145
Sp. Def: 90
Chandelure is more of a Special Attacker (given off it's massive base Sp. Atk compared to both Charizard and Mega Charizard X), and it has mediocre HP, Atk, and Spd, making it's (somewhat large but short) impression of threat dwindle down. Once this thing is low on HP- or the attacker has an upper-hand- you better kiss this flame candle good-bye, as it deals massive damage due to it's small Defense (but not mediocre enough). However it it does survive, it's a big threat.
Let's at least see what good move Chandelure can work with:
Will-O-Wisp (not really recommended)
Inferno (not really recommended)
Solar Beam (not recommended)
Lastly, let's split up the EVs.
Sp. Atk: 252
Sp. Def: 158
Splitting up the EVs like this gives Chandelure a chance to survive and hit to opponent with it's massive Sp. Atk.
Either way, both Pokemon are really good. However, one specializes in physically attacking and speed, while the other specializes in specially attacking at the cost of it's speed and defense. If I were you, if you're going to making your team all-out physical attacking, I would recommend Chandelure as support for a physically bulky opponent. If you're going to make your team all-out special attacking, I would recommend Mega Charizard, as support for a specially bulky opponent.
Hope I helped!