Ran into Rachel Pearl at a party a couple of nights ago and she handed me her new card...
This blog post will focus on the middle option -- Spotify!
I know a lot of musicians feel like Spotify and services like it are taking away from album sales, but there is no better way for people to start consuming your music quickly. If your music is on Spotify, and I think it should be, don't you want people to listen to it? If so, why not make that as easy as possible?
How you do it doesn't matter. Are QR codes dead? I don't know. It's tougher and tougher to get people to use them when they have no idea what's on the other side, but if you know you're going to get the music you want to listen to, they could work. That depends on your audience, of course.
If you (or your audience) aren't into QR codes, another way to easily get people to your music online is to spend $9 for a domain or make an easy-to-follow link from a domain you already have. For example, ListenToBandName.com or BandName.com/listen.
My point in bringing up Rachel's card isn't about whether you use a QR code, custom domain, or another method to get people over to your music -- the point is that you need to get people over to your music as soon as possible because that's how you're going to get new fans. With more and more people subscribing to "all your can eat" services like Spotify, why not point them in that direction?
More thoughts on the card... It's good to give people options. If they like the music, they can keep in touch via Facebook. Or, if they really like it, they can buy a CD. But get them to the music in the easiest way possible first!