On the topic of themes, please don't just pick a song just because its a good song. Not all good songs are good theme music and not all good theme music are good songs. Also, personal preference here but I HATE real wrestlers music being used in the leagues.
Try to find a song that fits with your character. I have tried this for each and every one of my characters and honestly, out of all the characters in the leagues I don't think I've found a more fitting song for a character than Buster Gates with My World. It's cocky, its arrogant, it's exactly what Buster is to a point. It's perfect. The only song I feel that is up there on that level is Brycey with both theme songs he's used. There's obviously some characters in the leagues who have songs that would match their characters but I dont think any are as perfect as the ones I've just mentioned.
Going back to my point again, My World for Buster Gates is not the type of song you could listen to on repeat (unless you're me. I do that constantly to get into the Buster Gates mindset before writing a promo), it's not the type of song that a lot of people will find great either, but as far as wrestling themes go, I think it's perfect.
There's also two types of good themes to use. 1 I've already mentioned is the ones that fit the character perfectly, the other is the songs that grow on you over time and make you think of the wrestler instantly. Edge is a perfect example of this. His theme doesn't really have anything to do with him, it's just a song, a GREAT song that over time the second you hear it you think of him. Other people to fit into this category are Batista, Christian, Sheamus, Bray Wyatt etc. The people who have good songs that fit their character are people like The Undertaker, Kane, Shawn Michaels, John Cena, CM Punk, Mark Henry. This second list barring CM Punk's Cult of Personality, aren't exactly the type of songs you could listen to, but they fit their character. This is what you need. Hope this helps.