I have an afghan that is washed regularly (because my cats shed all over it) and was made with Red Heart yarn about 20 years ago. It has not pilled at all. I have another scrap-yarn afghan made with all sorts of acryllics that I had in my stash - it has also worn well. From experience, I would recommend using Red Heart Soft or Caron Simply soft yarns for their durability and washability - plus, they're affordable when you're talking about the amount of yarn that goes into an afghan.
I recently bought the Comfort Knitting and Crochet Afghans book, which uses Berroco Comfort yarn for all of them. I'm making a sweater with it, and I love how it feels. But I don't know if it pills or how well it holds up.