Hello, I am a long time Silent Hill ... connoisseur, I guess, so I can share some info with you. So far, I have played, 1, 2, 3, 4, 5 to the end, and parts of the others.
If you want to go chronologically, you really have to start with the first one, which may be a bit of a problem, since it's a PSX (that's right, Playstation 1) game, and here you have two options. If you own PS3 like me, you can buy a version that runs on PS3, but looks just like the original (ugly). Or you can get the image of the game somewhere out there and use a PSX emulator like ePSXE or Xebra, which is what I did, and play it with anti aliasing, texture filtering and other bells and whistles.
2, 3 and 4 should run on contemporary PCs without problems, since there are native PC versions available (but all are console ports, of course). 4 is IMO also the last good sequeal (hardcore fans don't like it, but I did). Homecoming is utter crap, both technically and gameplay-wise, and so is the last one, Downpour.
There are also two other titles - Shattered Memories and Origins, both have versions for WII and PS2, and none of them run well in emulation, particularly, the flashlight effect is broken. I have heard there is a version of Dolphin emlutor floating around that runs both in playable state, but I did not check it out yet.
Silent Hill 2 is best of them IMO, followed by 1 and 4 (at least for me).
Shattered Memories are supposed to be good, I did play through the very beginning in Dolphin, it seemed good.
