Well, airline tubing may be more prone to cracking, though I've never used it with CO2. More importantly, however, is that most tubing advertised as CO2 tubing, or recommended for CO2 tubing, is 1/4" OD, 1/8" ID. And most fittings are designed for that particular size (though ADA and some other Asian stuff is 4/6mm). And any airline tubing from a LFS will be 1/4" OD but larger ID (something like 3/16"), which means it has thinner walls, and can't be used with certain connections.
So I wouldn't worry about changing out your tubing unless there's something wrong with it. But if you do decide to upgrade, any 1/4-1/8 tubing will likely do the trick. The Tygon stuff from USPlastic is popular (I use it as well).