I feel I'm beating a borderline-dead thread... But please cut some slack- I'm new here, and this is the most open thread in the forum (/singular board I signed up to participate in).
Disclaimer out of the way, my absolute favourite system is Dogs in the Vineyard
. The rules set (wikipedia link)
is beautifully minimal, intriguingly unique and fitting to the western genre. I especially love the custom feats, and how freeform the game is. I love how the game is designed to be played co-operatively- actively defining the line between player and character- so a character's secret, evil backstabbing plan may be played to full effect- or a conflict is resolved in a way which best suits the story- it's completely communal, and built to avoid rules-lawyering and selfish gameplay.
Coming a close second is Old WoD. My first adventure into Tabletop RPG's was Vampire: Masquerade (followed by joining a Requiem LARP- please don't judge me). I have to agree, the system is quite nice. I love the absolute freedom the Old WoD series gives. And the rulebooks were amazing. Beautiful and immersive and engrossing. I love that each clan book is written from the perspective of each clan- leading to conflicting Lore and adding realism and subjectivity to gameplay. I actually like the darkness in these games. That there is no 'lawful good', or 'lawful evil' - but futile victims of their foresires trying to make the best of their immortality, and fighting a losing battle with their beast.
And my limited experience with the 40k pen and paper systems has been simultaneously infuriating and delightful. I love how Dark Heresy seems designed against the stereotypical 4ed "I win!" mentality. I love that at least one member of the party will end a session horribly maimed- but (usually) stronger for it. I love that even though they're still stronger everything
in the universe is a serious threat- especially their employers. I agree the % system is marvellous. The ciritcal hit charts can also be fun...
My only real experience with D&D is a 4th edition campaign- so I won't comment on the on-going version debates.