Help with "ease" on my first cardigan?

Because my LYS had a yarn sale today only, I went and bought yarn for a new project that I don't need to start on (but am going to because its so darn cute). Anyway. The pattern here says "this garment was designed with approximately two inches of ease". The sizes are such that one size is a size 38" bust, and the next one is a 42" bust. I'm a 40" bust. So my question is with these two inches of ease, which size do I make? I generally like my cardigans slightly baggy, but not too baggy. I tried to look it up on Google, but only wound up slightly more confused. Help me, Knittit?