Their hexagonal version was the easiest. Their Bridges version was interesting, but still not very challenging.
Unquestionably, these puzzles are the hardest and most fun. I'm doing these while watching tv.
The section I like most is the Warpyard Park. Of the 150 puzzles, I thought the hardest were 109 & 145. In the Jumbo Jet Pack, level 123 remains unsolved.
Every cell must be filled. This fact actually offers many clues that I utilize.
Interesting feature: some cells can only be crossed with a specific color.
Minor complaint: there are 2 shades of red that are a wee bit too similar. Same for the whites.
Getting back to the whole Flow Family Puzzles: they've been downloaded over 250 million times. That alone helps turn non puzzlers into puzzlers. Kudos to them for that, and this game Flow Free: Warps. This version has about 1200 FREE levels. Some go very fast. I am going to do them all.
High Praise: I paid $2.99, not to skip the ads, but to show gratitude. There are about 2000 levels. At the moment, I've solved about 1400 levels, plus all of the daily puzzles for 31 days in a row.