Final Fantasy 12 is the closest you will come to Kingdom Hearts in the "main numbered" games. 12 has some serious fucking problems with gamefaqs being almost mandatory due to all the cryptic "let's sell a strategy guide" bullshit fueling the whole game, but the combat is A+ even though it still uses an ATB type system but outside feels a lot like Kingdom Hearts. Just don't expect a competent story progression since they pull the "go from point A to point B and have no pay-off" card about 3 times in a row for the majority of the game's running time. It is actually a good story, but the actual progression you play is poor. I don't really know how they fucked it up so much, they had a great world yet the linear path they force you down misses EVERYTHING they could have added.
Anyway, the best turn-based Final Fantasy is FF10 hands down as an established fact (Buy the PS2 version is is vastly superior and cheaper since the "HD remake" is barely even noticeable without side-by-side comparisons and the updated music is absolutely shit, it is the "let's make a remix by adding more instruments instead of actually properly remixing the song" type "remix" so as a result sounds like an amateur got the original song and added random shit on top to ruin it, hell the "Challenge" track is made to be techno in the remix FUCKING TECHNO FOR THE UNDEAD LADY BOSS FIGHT, how could they fuck that up so badly? TECHNO ALWAYS GOES WITH MECHANICAL THINGS! THAT IS HOW MUSIC IN GAMES WORKS! Fucking incompetent idiots. Seriously look at any good game, Skies of Arcadia that has a lot of techno themes since there is a lot of mechanical stuff in that game like the Gigas, but they also don't use techno for the rest of the game since the rest of the game isn't fucking mechanical! I know I am banging on about the same point here but people actually praise this fucking remixed soundtrack TECHNO FOR AN UNDEAD FIGHT! How can anyone fucking approve of this butchering of the original great sounding music?)
The best ATB type game in the series comes down to preference, if you want to chill without thinking much about the fights then pick 7,8 or 9. If you want to push for ridiculous speeds and for the combat to be exhilarating then pick 13. 13 is definitely the most "active" ATB game in the series with being able to time attacks for them to interrupt the enemy's attacks or land at the same time as your allies' attacks being a key improvement that doesn't exist in the more chill previous ATB games. But as a result it does need you to be more alert and focused as a result so if you want to chill 7, 8 and 9 has you covered....well questionably 9 as it can be bullshit hard at times.