When we purchased our sofa, it came with a white slip cover. I usually use it spring-late summer then switch to the Svanby Beige (which I don't think they carry now?). I like both slip covers equally and really could not choose a favorite. The white is lovely and fresh for spring/summer and the beige has a little more texture and the warmer color is nice for cozier months.
Let's start with the Ektorp in general. On any given day (at least before college started) our family room looked like this. Our son and his 6'+ friends like to hang out here. (I love this, BTW.) Even though the Ektorp isn't marketed for larger people, you can see that they all appear to be pretty comfortable, right?
Let's talk about cleanliness, shall we? If you have a sofa that does not have slip covers, this is not meant to make you feel dirty. It is simply to demonstrate how gross humans are. All of us. I took this picture after a certain family member mowed the yard then sat down on the sofa. Some would say that they do not want a sofa that shows dirt. They make dark slip covers for those who prefer not to see it. I say show me the dirt because I want to clean it. Luckily this dirt was easy to wipe off, but sometimes we have spills and general yuck after about 6 weeks of use so I throw the slip cover in the wash and in a matter of hours we have what seems like new furniture. To me this is invaluable! Tip: Wash slip cover in one load, then cushion covers in the next load. It is just easier and it gives the slip cover a chance to dry if you remove it from the dryer while it is still damp (which I recommend). If you do this you will avoid having to iron. Another tip: Do not let the hot iron touch the non-woven fabric on the slip cover. It will melt :).
(the looks she gave me Halloween night when the kiddos kept knocking on the door)
Here is a close-up of the Svanby Beige. It has a more pronounced twill pattern than the white slip does and the color is warmer for fall/winter.
Storing the extra slip cover. I was worried about where I would store the additional slip cover when I bought it, but then thought about a space saver bag. I found this extra large one at Bed, Bath, & Beyond which is perfect. It holds all the pieces and slips easily under our bed. After your slip has been in storage you might need to iron it :(.
Would I change anything about the Ektorp? The only thing I would change would be to have an option for one or two cushions across the bottom and back rather than three. Something like this or this. We will most likely give our Ektorp to the college student and upgrade eventually, but overall, my entire family loves this sofa! No one paid us to say that.
And while we're on the topic of slip covers, have you ever heard of Bemz? They make slip covers for most IKEA furniture with lots of patterns/colors to choose from.