I've done Nashville, the music is amazing. Austin, TX as well.They are different, that's for sure. Vegas is bigger, more expensive, and has gambling. Nashville is geared toward live music (most of it really good, and I don't even like country). If you just mean Vegas is bigger, sure, it has the advantage. Otherwise I'd say Nashville is every bit as much of a party town, if not more so. I do like Vegas too. The architecture is amazing and there are some great restaurants and shows.
You should give Nashville a try. You may enjoy yourself.