Neither.

The one on the right runs a significantly non-trivial chance of a rolled ankle.

The one on the left is purely slip-in, with no way to use the toes to anchor the flip-flop onto the foot.

I’m taking right/yellow. Thankfully those sandals have a little loft while she’s bent over like that so she’s perfectly positioned for a drink from the fire hose!

Green

Left

Yellow

Yellow

green

Going green, but that’s a tough one

If one is just considering sandals yellow is better. However, for everything else green is nicer. Not to say yellow isn’t nice of course.