I was contemplating really hard just like you are right now... But decided to go with the mini as I've been waiting for the retina version for a while now.
After playing on it for 3 days, I think I've made the right decision. If you go in the store and compare mini vs air, you'll be tempted to get the air over mini since the weight difference isn't as dramatic and the screen real estate and the font size on the air is incomparable when seen from side by side.
However, what you don't realize is air even though it is extremely light, it is really difficult to use in an outside setting due to its large size. Reading on a full sized ipad seems perfect in your living room, even in your local library, but in other public places like the subway and cafés, it just looks and feels awkward to use. The font size may seem like it will be an issue when you compare with the air, but really is a nonissue when used independently as the retina screen allows the texts to be completely legible... And there is always the option of pinch and zooming.
Finally if you're going to take the ipad outside, I'm assuming that you'll be putting it in a case, and mini with the smart case is obviously a little heavier than the one without, but is still light and portable. I don't know if if I can say the same about the air.
Having said all this, it is really your personal preference, but I hope my opinion helps in this happy but frustrating decision to make!