There are are so many things to consider when shopping for a sofa; it can be easily overwhelming. Here are the things I consider (in order!) when sourcing a sofa for my clients:
Aesthetic - the way the sofa looks is first and foremost. I firmly believe that you can find a comfortable and durable sofa that also fits the style of the room your decorating. Many people think of comfort first and may end up with a super comfy but ugly sofa. I don't think you have to compromise!!
Comfort/Lifestyle - if you're planning on spending a lot of time here, this should be very important. Consider what you'll do most, socialize? lounge? entertain? nap? eat? read? watch TV? all of the above? This matters when considering the depth of the sofa, the density of the back cushions (are they movable or not?), the fabric you may choose, the size/shape etc.
Footprint - the size and shape of a room really impacts the type of sofa you can/should choose. I had clients steadfastly committed to the idea of an L shaped sofa, but have a super narrow living space. When I mocked up a floor plan they saw how little room there would be to walk past the sofa and the wall. Not all sofas are created equal. They come in MANY different lengths and depths. Be sure to check the dimensions and if possible actually mark out in your space where the piece will sit to get a feel for it.
Here are some photos of sofas and rooms that have inspired me, that I’ve lusted after, and some that I’ve included in projects. (These photos are not mine, and are included as inspiration only!)