I think Tangled win when it comes to storytelling. I think it get generally flows better. Also the fact that Tangled was a bit in a production hell for a bit and the animation had to be reworked several time. I think they were able to take the time to develop it to work well.
Frozen story however is a bit sloppy. I think it became more popular because the songs were catchier and Olaf is more iconic than the sidekicks in Tangled. Similarly, the story was rewritten several times with the final one being written around the song "Let it Go".
My personal fixes in Frozen...
-I really wish Elsa running away happened after her parent's died and have the story of her living in the mountains for several years. Instead of the freezing being instant, it is instead something that happens over several years. And when Anna leaves to investigate, she is shocked that it is her sister that she hasn't seen for years.
-Don't make Hans a surprise villain. I think Hans would have been far more interesting if he was someone who thought his bias against Elsa was for the greater good. He doesn't care about being the ruler, he just wants to protect everyone. I think Anna and Hans falling out should have been on them disagreeing on how to handle Elsa. Hans would make Anna seem like the bad guy because her plan could end up hurting many people. And when Hans tries to do things his way, it eventually leads to him dying. Anna is seen as the hero in the end because she choose compassion over fear.