How do I choose the right brand of slip covers for my sofa?

I dont have a specific brand, but I will say that you should look for one that will fit your couch the closest. I've gotten the big "blanket" covers before that fit numerous sizes, but you have to constantly tuck them in and they look terrible more often than not. It was cheaper, so that is why I got one like that, but regret it. Spend the money on a fitted slip cover for sure!

Can you post photos, so we can see the type of furniture which you have please.

Depends on use of furniture what type,style,color,material you should get. Pets,kids,family room,indoor,outdoor,washable(these all need durable easy to clean materials) denim (you could dye white covers)https://www.pinterest.com/pin/60517188721482381 high end looking-formal http://www.loose-covers.biz/Gallery1%20Formal%20tailored%20covers.html info on selection https://www.decoist.com/2012-06-13/selecting-high-quality-slip-covers/ solid piece,cover with separate cushion covers,colors of room decor(some only come in certain colors),printed to hide more stuff from kids-pets??? One thing I recommend is no micro-fiber it snags & is a magnet for pet hair.

I agree with Maura. Unless you find well fitting/custom slip covers, they can appear to present a very dissheveled look in a living room/family room. If this is for a basement or an area with children, look for something durable and washable, that will remain securely in place.