I buy cotton/modal fabric tops a lot. It's my favorite fabric. It holds its shape and color over time. And the fabric feels a bit silky to the touch. In my experience, it doesn't shrink at all with washing. I don't know about drying, because I hang up my tops to dry.
A rayon blend can be more unpredictable. I've had blouses, tops and sweaters with some rayon in them that have kept their shape beautifully. I've had others that shrank. Good brands of clothing are less apt to shrink, in my experience. Also, a small amount of rayon is less apt to be a problem. But I'm still a little suspicious of rayon.