Most people buy a soft rug by how it feels in the store, standing on it in socks for ten seconds, and never think about what it looks like after six months of actual feet, actual spills, actual life. That's how you end up with something that mats down in the high traffic spots and looks fine everywhere else.
Color wise, the easiest rugs to live with are the ones that already look a little lived in: oatmeal, warm gray, a muted clay, something with a bit of fleck or tonal variation in the yarn itself rather than one flat shade. A solid cream rug photographs beautifully and shows every single thing within a week, coffee rings, dog paws, the dust that blows in every time someone opens the front door. A busier pattern or a mid tone with some movement in it hides daily life without looking like you were hiding something. As for what separates a good one from a bad one, it comes down to density and what the pile is actually made from. Pick it up and check the backing, a well made rug has a tight weave and you shouldn't be able to see the floor through it when you fold a corner back. Wool and wool blends cost more but spring back after furniture sits on them for a year, where a cheap synthetic pile stays flattened in two neat rectangles where the couch legs lived. Run your hand against the grain, decent ones have a consistent feel all over, no patches where the fibers feel thinner or looser. A soft rug does not belong anywhere near a muddy entryway, a kitchen sink, or under a dining table with small kids and spaghetti, those rooms want something flatter and washable instead. For sizing, measure the room before you fall in love with anything, and in a living room the front legs of every seating piece should rest on the rug at minimum, with all four legs on it being the better outcome if the room allows it. Leave a gap of a foot or so between rug edge and wall so it reads as a piece of furniture rather than wall to wall carpet, and in a bedroom, go a size up from what feels necessary so it extends out past both sides of the bed, not just a strip peeking out underfoot.
These rugs reward a little patience over a lot of scrubbing, and a good one still looks right after a move, a new couch, and a toddler phase.
Vacuum in both directions every week or so and the pile stays upright instead of flattening into permanent furniture tracks.