Corniglia, is the only town that sits up on a cliff, offering great views, but no sea access. The train actually stops at the bottom of the hill, so you have to either zig-zag your way up the street or take what I call the death stairs, which consists of 382 steps. Somehow, we managed to avoid the death steps on the way up, which I was thankful for. Corniglia is by far the least touristy of the towns, and the smallest in general. It's nice for a quiet escape from the crowds, and the hiking to and from is some of the best.
Vernazza is probably the favorite town of most tourists; it sits by the sea with a couple of small beaches, offers a lot of waterfront dining, and is really picturesque. But of course, that means it is one of the most crowded. There is also a tower - Doria Castle - that we paid a couple of euros to see. The tower offers great views, but then again there are great views everywhere, so it's not a necessary stop.
Monterosso is by far the biggest of the 5 towns and is pretty much completely flat at sea level. It has the most extensive beach, which spans the length of the town. It is divided up into two parts, one being mostly hotels and housing, and the other having more shops and restaurants. The hotel side has very little to do, though the beach is larger, so I'm sure it's super crowded in the summer. To me, Monterosso is the least unique of the towns.
Riomaggiore is the southern most town, and from what I've read is one of the least exciting towns, but I quite enjoyed the town this time (last time we were really only near the train station). The town starts high and the street descends towards the sea, and there are a good amount of restaurants and shops. My favorite part was the little beach, which was a short trek off to the side of the town. It felt like the most intimate of the beaches and the least crowded. Tho, it was pretty stony, we could've hung out at this beach all day, really peaceful.