I'm not a fan of the free-to-start model, but my favorite is definitely Rumble World. It feels more like a real game than the other two, and it helps that you can max out your purchases and then essentially "own" the game. I would rather have a physical copy, though, but at this point, I've sunk a bit of money into my digital version, so I'll stick with that. I haven't paid the full price to max out my diamonds yet, though, so I'll have to see if I want to finish doing that or not. I have a hard time staying motivated to play free-to-start games; I'm always afraid that I'm about to get screwed over.
My second favorite is probably Shuffle. I liked it at first, but at a certain point, it started to be too many weekly updates to keep track of, and I didn't really like a game where I had to play for 15 minutes at a time and then take a break. I missed a couple of weeks due to traveling, at which point, I gave up (because I'm too much of a completionist, didn't want to deal with figuring out how to get everything I had missed, and realized that I really wasn't enjoying playing anymore anyway).
Picross was a major disappointment. Sure, I guess I can unlock everything with enough money, which is a nice plus, but to me, it doesn't feel like it's worth that much. I also don't really like repeating picross puzzles (they're static, so once I've solved them, I've solved them), and seeing how that's the only way to earn paltry sums of picrites to advance, it didn't feel worth it to me. The Pokemon element also felt like an added bonus to me, rather than an integral part of the game. In the end, I've only played it for one or two days, but I have no particular desire to go back and continue playing it. Which is sad, because I generally like puzzle games, and I like Pokemon.
Diamond FC: 1504 2172 1147
White FC: 1721 2860 5156
3DS XL FC (X): 2466-2669-5197