I jumped in with Homecoming and Origins, but since backtracked and played the rest of the series. Out of the original four games, I have the weird list of:
SH3 = SH1 > SH2 > SH4
Maybe it was because among the originals, I played Silent Hill 3 before Silent Hill 2, but that one was definitely more memorable to me (not to say Silent Hill 2 isn't memorable). In any case all the original games are god tier Survival Horror that, as far as I'm concerned, trumps all others.
With regards to all non-Team Silent games:
SH0 > SH5 > SH: Shattered Memories > SH: Downpour
Silent Hill: Origins always felt the closest to the originals in terms of gameplay and atmosphere. Despite it's bizarre weapon system and lack of originality, it's hands down my favourite non-Team Silent game. Silent Hill: Homecoming comes up next mostly because it was my first Silent Hill game. The story is just alright, the combat is closer to Silent Hill than the next two games, but it's also not that great. The idea of bringing back Pyramid Head purely for fanservice irked me too later on (despite being a great hook for a newcomer).
After that game, it all went downhill. Shattered Memories has a great story, and is a worthy reboot in that regard, but my God was the gameplay atrocious. Walking around and exploring was okay, but combat is non-existent and the monsters lack any variety. Downpour is just as bad, at least giving the option for combat, but with absolutely atrocious monster design that belongs more in the Condemned series than anything. However, the technical faults of that game simply ruined it for me, even post-patch.
While we're on the subject of Silent Hill, has anyone purchased any of the Gecco figures? I recently picked up the newest Heather Mason figure and am eagerly awaiting it's arrival. I sadly missed out on the Red Pyramid Thing though.