If you’re trying to make something realistic, it’s best to just add an extra edge (two actually… one on either side of the edge you want to look ‘creased’). There are tools in Blender that can get you quicker results, but there are also drawbacks to those features:
Crease looks good, but it’s dependent on the level of subsurf you apply it at. If you make a crease look really good at level 2 subsurf, but render at level 4 the edge will look slightly different. Also, if you plan on exporting the model the crease will be gone unless you apply everything and export a fully subsurfed model… not ideal. (note, i haven’t used the crease tool since i first got blender something like two years ago… it may have changed, but i still don’t use it)
Edgesplit can look good as well, but it makes an infinitely sharp edge. This sort of edge is impossible in the real world, so it can look great for very small objects, or for when you’re a far distance away from something, but up close it will lose it’s realism. Real-world objects’ edges are ALL rounded to some extent, even if they look really sharp. Unless you are making a Sub_D model of something like a sword or razor-blade or something similar where you really REALLY need a sharp edge, you can get better results usually using edges. Light will not get caught by an Edgesplit edge, and thus you will lose out on highlights on the edge, etc.
The reason I say to add one edge to each side of the edge you want to be sharp is due to the way the Sub-D algorithm works. By using 3 edges instead of 2 you guarantee that no other part of your model will be distorted, whereas just cramming two edges right on top of each other can make for some unpleasant bulging or dipping in areas near the crease. Having one edge on either side allows for the maximum amount of control for how sharp the edge looks. You can get away with two most of the time, but I find three edges makes the low-poly mesh look a lot more solid and easier to work with. But that’s just my view.
As far as the image / model you posted, you could technically have used nothing but 90 degree angles if you were going to subsurf it, tho if you had planned to unwrap it there would probably be some heavy distortion in the texture. with procedural textures, tho, you could get away with it.