FF1 is a good introduction to JRPGs in general if you've never played one before. You can choose 6 classes to assemble your four-man party, and you can have as many of one class as you want in a party (e.g.: Warrior, Warrior, Warrior, Warrior in a single party). Highly recommend playing either the GBA remake or the remake for PSP (it might be on mobile too? Not sure, I played the GBA one), as it fixes a lot of the issues with the NES original, such as giving mage characters an MP meter instead of limiting spells so you can only use them a specific number of times.
FF6 I've not played yet (though I own it…), but I've heard the storytelling is very good, as well as the battle mechanics.
I didn't grow up playing FF7 like a lot of people did, but I bought it for PS4 two years ago. Got past the first boss, then stopped playing a bit afterwards. The graphics bothered me a bit (especially the backgrounds), but I might give it another go sometime.
FF13 is meh. I almost beat it to the end until the disc got fucked by my Xbox. It's been 7 years since I've played it, but I remember it being very linear. There were side quests in the game as well, but I literally don't even remember completing one?
TL;DR: Recommend FF1 to learn about JRPGS and basic FF mechanics if you've never played one (play the remakes, not the NES version). I guess I'd also recommend FF6 as well, by word of mouth saying how great it is.