Okay, well if you want a more bulkier choice you should stay with Ninetales, since Chandelure and Houndoom are terrible defense-wise. If you don't though, this is gonna be a Chandelure vs. Houndoom thing.
Chandelure vs. Houndoom
Chandelure and Houndoom hold a fight with Sp. Attack. Chandelure has an impeccable Sp. Attack stat that Houndoom doesn't reach even through Mega Evolution. But even overall, a Mega Evolved Houndoom vs. a Normal Chandelure have almost even stats.
I would choose Houndoom.
Houndour evolves earlier than Litwick, who evolves all the way up at Level 41. That would evidently take a while, whereas Houndour evolves at Level 24. This would be a lot more convenient since Litwick isn't the best Pokemon to use.
Chandelure also has a more diverse movepool than Houndoom, but both still have access to Grass- and Electric-type moves that will defeat Water-types. Houndoom has four weaknesses and Chandelure has five, and Mega-Evolved Houndoom has a higher BST. So I would choose Houndoom, but it's purely your choice.
Houndour can only be found in X at Route 10, and the Houndoomite can be found in Route 16 between 8-9pm.
Hope I helped. :)
Sources: Serbii's respective Pokedex pages, this