If it wasn't obvious already, I'm partial to SH2. I liked that it took a step away from the rusty, veiny otherworld and used typical environments we'd see, except darkened them and added fog. In the other games, where it takes you to the otherworld, there's a separation from reality, whereas in SH2, the reality is that there are literal and figurative monsters there.

There's also the psychological aspect of the in-game characters that bring a new, unique level of horror to the game. When you begin to realize that James is not only responsible for (SPOILER)Mary's death, but also that the terrifying images he sees are a direct result from his sins, it makes you question (well, it made me ) just what kind of monsters you have hidden inside you. James never came to terms or accept that he had these monsters (masochism, rage, etc.) inside and they almost devoured him. The idea that our own monsters can come out and torment us is what is scary.

I enjoyed SH3, too, regardless of how irritating Heather was at the beginning, but I think what makes me lean towards SH2 is the amount of depth found in the game, added onto, of course, that I feel SH2's scarier.