Guest Posting

Hey guys, I have 5 easy keywords I want ranked. My competitor is dominating the first page with crappy backlinks. They have their FB page, main page, and inner pages on the 1st page. I was going to buy relevant guest post with DA 20+

Should I use my main URL and 1 keyword for all 5 guest post (post are on all different websites). or should I use my main URL and 5 different keywords for the guest post?

Suggestions?