Which one of picture related should I buy, /v/. Having in mind that I wanna have
Played both here, it's really up to preference. Fantasy life is kinda like "Runescape" for the 3DS, while Yokai Watch is like "Dragon Quest Monsters GBC" for the 3DS. If you've played either of those you'll understand what I mean.
Do you like Animal Crossing? Fantasy Life is just like that, but with a huge checklist. It has a bunch of pointless quests you can do. I personally got bored of it very quickly, but if it's your kind of thing, give it a go.
Yokai has a demo you can check out, haven't played it yet.