Of the three so far, I find LEGO the most enjoyable as far as game play.
I think Lego Dimensions has the most solid 'game' center, which makes sense as they've been making those games for like 10 years now. But it also feels like, of the three, it's the one where your character choices matter the least. They just unlock little collectables here and there and otherwise don't matter much. It's still good though. I want to see how they expand this as it grows into it's own thing in the future.
The Skylanders games have been improving over time (the first game was kind of bland but they're pretty respectable now and the newest one has a great look to it) and they have the biggest roster of characters but of the three I feel like they're the most condescending to kids. They just made the big mistake that the Lego games make sure to avoid, and that's appealing exclusively to children to the point of alienating their parents(or in my case older siblings) who might want to play the game too. Which isn't really a problem for the franchise itself, I don't want to come across like I'm being all "this kids game should appeal to me, the adult playing the game" because that's ridiculous but I think there's still room for improvement and it's biggest strength is the game's roster size and variety.
Side-note: Where the heck is the Skylanders cartoon series? Way overdue by now and a very natural fit for introducing new characters and gimmicks each season alongside the new games.
Disney Infinity by comparison to those two is, I think, the most 'complete' package in terms of having good character variety and lots of stuff to do. The only issue is that there's no built-in 'use anyone' storyline core to the game like Lego Dimensions has. But the content creation tools and huge amount of free player-generated content available make up for that to some degree. They're leveraging Disney's properties really well though and I'm looking forward to seeing the series continue to improve over time. 4.0 is pretty highly anticipated for me just because it'll be the first release that's theoretically not centered around one of their big pillars so we could see something new and neat there.
I'm really glad that all three Toys To Life games are pretty fun to play though.