Which is easier?

Hey!

I was looking to create a new site but i’m not sure which theme to buy and change. I have a theme that represents what I want it to look like. Then I have a theme that has the payment options and features within the site that I like.

My plan is to pick one then change the coding on it to include characteristics that I want from the other.

Would it be easier to change the way the theme looks or how it functions?

I guess it might depend on the factors but I am looking for a general answer.

Thanks!
Jon