It's funny that people are picking Jasmine. Ariel and Merida have a LOT in common in their stories (both taking risks and making magic spells with witches in exchange for an item of value), and Ariel actually got to get herself free from underneath her father's thumb. Jasmine attempted once and failed. Merida may like the whole "I am not a prize to be won!" speech by Jasmine, but Ariel is just as, if not more, rebellious.

Yes Merida and Ariel are both rebellious and against their parents a lot but they have very different reasons. Ariel fights for a guy she loves and Merida fights for herself, and later for her mother. Merida and Jasmine are have a lot of common too, they both forced to an arranged marriage by their parents and kingdom, and they're against it. Both are also outspoken and express their opinion harshly.

they would be neck-to-neck when it comes to compatibility with Merida. Both have similar traits/situations that Merida can connect over -outdoorsy, outspokenness, trapped in their world.
I pick Jasmine coz she wasn't ready to get married for the tradition of it. She wanted a reason. Ariel could come across too romantic for Merida's taste. Jasmine wanted to experience more roles of a princess just like Merida, except being a pretty, feminine figure. Jas wanted to do things on her own and not be told what to do, how to behave which is what Merida also felt restricted about the most.

I think she'd see Jasmine as able to talk the talk but not walk the walk. She acts strong and independent but does need Aladdin's help a lot and I think that would irk Merida. And Merida wouldn't judge Ariel's actions as negative at all; she'd completely relate.

Ariel was brave enought to decide her own fate, Merida'd admire that in her.