Final Fantasy III DS is a beautiful game visually and aurally, but the gameplay is still TOO 8-bit. Leveling up in jobs simply makes you better at that particular job; unlike the later Final Fantasy V, you can't use any skill or benefit from one job in another. Basically, that means you'll probably stick with one kind of job for each character until you get access to a better version of it and ignore all the rest. The game also has its old school difficulty, in that save spaces are seldom and there are many boss battles where you will get MAIMED.....and since it's a pre-SNES Final Fantasy, battles are turn-based instead of ATB. I'd recommend it to only the most hardcore of RPG fans, who enjoy lots of Game Overs but little reward.
Kirby Squeak Squad, on the other hand, is just like most of Kirby's other 2D platformers except it has touch screen elements for mixing stored abilities and minigames and stuff. The minigames are nothing special though, and there are only a select few abilities you can mix, so it's basically like most other Kirby platformers.
As for what I would recommend, it really depends on your tastes. If you want another Kirby platformer that isn't quite Kirby Super Star but is still a new Kirby platformer, go for Kirby Squeak Squad. If you want a visually and audially appealing RPG that has a difficulty level that will make you scream profanities and throw your DS across the room, then go for Final Fantasy III DS.