Depends on your style and natural hair color. Do me the middle one would look best but if I had black hair I would love to get the blue in there. But the first one is simple and pretty and in style and isn't too extreme
I really love the first one, as it looks the most natural and is probably the most versatile. Like you could very easily add hair chalk or some other product to the ends to give you any color sombre you like and then just have it wash off. But if you love one of the above more than the others you should go for it! It's just hair, it will always grow out or you can change it back whenever you want. If you love mermaid style hair then rock it!
I voted for the brown to blonde ombre, since I've had that one before. I do like dying my hair red, but for fall so that could be a good option, too. The black to blue is pretty, but I don't dye my hair unnatural colors usually.
First of all, yesss spring!!! finally! is gonna be warmer xD... but now, lets talk about the hair haha. I like the first one, buuuuut is common hehe, so maybe you could try something risky and go for the second one or last :0