OMG, I can't believe you just posted this. I am just getting ready to call someone to measure for new slipcovers. We currently have and have always had slipcovered furniture. I found it completely necessary, even before we had kids, because we really live on our furniture and we have a dog. That said here is what I am planning on doing.
I change the room around with the seasons so we have always had spring/summer and fall/winter. If you are doing slipcovers I would highly recommend it. They will last longer and you won't become so bored with them. We have a Pottery Barn couch in our apartment and I do love it, but have to say that after washing the slipcovers they started to ravel in the seams. The couch is yellow and I wash it a lot. We also have a weekend house (which we are currently living in full time) and I have a Shabby Chic couch, which I have now had for 6 years and I LOVE it! The slipcovers wash beautifully. They are cream and the others are green linen. I can't say enough about the quality, however I can say they are VERY EXPENSIVE! The good thing about Shabby Chic is that you can order replacement cushion covers which is a really good thing because those are really the only things that wear out. We have two Mitchell Gold chairs and I really like them. I had them covered in a sort of brushed chenille and those have also washed really well.
I am now getting ready to have white twill covers made. Everyone thinks I am CRAZY, but I just love that look for the summer. For the fall/winter I will have something done in a deep cream (I think) and accent both with pillows. I figured twill and or a denim like material will hold up well, especially with washing.
We have a Crate and Barrel leather couch in our den in the apartment and I really like the quality of that as well. Not sure about their slipcovered pieces. You may also want to try Restoration Hardware. We have some of their wood furnishings and I am very impressed with the quality so maybe their slipcovered pieces are good also.
Keep me posted on what you decide. I am off to make my phone call!!!