So what's your favorite RPG and why do you like it?
Of the ones you haven't tried, my favorite is Chill, 2nd edition.
There are several things I like about the game. First, it does small scale intimate horror better than any other game I've tried. When you get killed in Call of Cthulhu, it's often as not highly impersonal. That's of course part of the horror of the setting, but in Chill evil is intimate, personal, and deeply is invested in your physical, mental, emotional, and spiritual destruction. This is the stuff of childhood nightmares. The other thing I like about the game is that it does a very good job of showing and telling you how the prepare the game and run it. This isn't merely a high concept game you read for the rules. This is a game that relies on a backbone of well written intricate modules to get you playing the game for real. Character creation is also a blast, since its a pretty elegant mix of a class based and point buy system, it helps you find a concept while giving you the tools to flesh out the character you want to play.
Another game that you should try is Star Wars 1e, in the D6 system. This is the system that best captures the feel of the movies, so that during the actions sequences you will be hearing the music in your head. While it's a completely different system than chill, the same basic praise can be heaped on it. The game does a wonderful job showing and telling you how to run the game. It has an a number of excellent scenarios. Character creation is elegant, helping to you to find the concept, while being flexible enough to encompass just about anything. The system isn't perfect, but it gets the job done.
Personally, I'm also fond of the classic Chaoism Call of Cthullu - 5th edition is what I have on my shelf, but there isn't a lot of difference between it and 3rd or 4th. The game is sufficiently lethal that it puts a high value on good roleplay and emersion, because really, you don't expect to survive combat. There are some odd quirks in the rules, but the system is very solid, character creation is fun, and the experience system that rewards you for what you do is as elegant as any ever produced.