Overall, using 이/가 indicates that you found something out by yourself, by experience (eg. you are wearing these dress shoes right now and you are feeling uncomfortable).

은/는 on the other hand provides the feeling of comparing (when used specially for comparing there should be an another sentence to have enough context. Here, as additional information it could be: "my old sneakers are so comfortable").

But hey, don't worry about that at the beginnig - I heard that Koreans write their scientific works about the differences between those particles :) So you can basically use 이/가 and 은/는 interchangeably.

I was told you just have to get used to when to use which and that there isnt a clear rule.

One is wearing something on your feet and one is wearing on your body.

I believe 신는 is used for things worn on the feet.