Which one is better?

I am struggling with which essay topic to proceed with.

Essay 1 : Soccer and how it has affected my personality/struggles through life

Essay 2 : Dancing with a group in front of the elderly, how it helped me open up and try new things

Essay 1 is more supported by the rest of my application (I have played varsity soccer), but I worry that writing about sports is much too common. Meanwhile, essay 2 is not supported by the rest of my application (I have never danced before), but this topic may be a little more unique.

Based on that ^, which essay topic should I focus on?

It depends on which topic you could write a more compelling narrative about. Really there’s no way to tell which is the better essay unless you have them both written.

With that said, you’re right in that sports are one of the most common topics people write about (sports, service trip to developing country, etc.) If you went with Essay 1 you would want to explore what makes your experience with soccer more unique/memorable than anyone else writing about sports.

So there is no concern with writing an essay that isn’t necessarily supported by the rest of my application? @Lagging

No concern - it could be a chance to show another aspect of yourself that otherwise adcoms wouldn’t know. Essays aren’t a place to show off achievements or ECs on your app but to show who you are. People successfully write about things as wild as Pokemon or a halloween costume every year.

The essay shouldn’t be a rehash of your resume. The essay is an opportunity to make someone think you’re interesting enough to invite to a small dinner party.

Only write about something if it’s going to be an ENGAGING story.