Upholstery covers should be chosen based on the interior design of the room, the amount of wear and tear expected, and your budget. You should make sure you are purchasing the covers from a reputable source, regardless of whether you are buying ready or custom made. It is probably a good idea to shop around and narrow your choices to a few pieces before you make a decision.
There are advantages to having your upholstery covers custom made, and in many cases, custom work may be the only option available to you. This is because you may have furniture pieces with a slightly irregular shape, in which case, you may be unable to find ready-made covers that fit. Upholstery covers that are ready-made usually come only in standard sizes and shapes, and even then, the fit has to be perfect or you will end up with a wrinkled or sagging covering. Custom made slipcovers will usually cost more, but you will probably get a better fit, and you will have many more options available in terms of style and fabric. Time frame can sometimes be an issue with custom work, so if you are in a hurry you should inquire if the work can be expedited for an additional fee.
If you decide to have your upholstery covers custom made, it is important that you have a written agreement that clearly defines the work to be done and a time frame for completion. In addition, make sure you understand what recourse is available to you in the event that you are unhappy with the finished product. One arrangement that seems to be a good option for both parties is to pay half the money up front as a deposit, with the remainder paid on completion. This will motivate the seller to finish quickly, and give you some protection if you are unhappy with the work.
Assuming you can find upholstery covers that fit, purchasing through retail establishments has some advantages. Retailers usually have standard return policies, and if you are unhappy with the covers after purchasing, you will typically have a few days to return them for a refund. In addition, you will not have to wait. In most cases, you will be able to make your purchase and walk out of the store with your upholstery covers in hand.
Regardless of whether you choose custom made or retail, fabric and design will be very important. Unless you are planning to redo the entire room, you will need to find pieces that coordinate with the room décor. Fabric content will determine whether the covers can be easily cleaned. If the piece will see a lot of use, it is probably a good idea to purchase upholstery covers made of fabrics that can be machine washed and dried.