Round are 8-way, there just aren't any corners to feel.
Square, aka 4-way/8-way, and have a very square feeling with definite corners.
Octagonal gives you slight corners, enough to know for sure you're pressing the direction properly.
Keep in mind with the U360, you can map it so the round can be 8, 4, 2, 49-ways, analog, or whatever way you want.
I prefer the round over the square. I have my frontend set to change the map so that I'm using the proper setup for each game, no matter how many directions the stick needs to go.