It's a tough call. For Single Player, I'd go with Doom 3. The graphics look great and really creepy. But Half Life is the king of online multiplayer FPS.
"Huard, gonna go back to throw the ball. Sets up, looks, throws towards the corner of the endzone...it is INTERCEPTED INTERCEPTED, THE DUCKS HAVE THE BALL! Down to the 35, the 40. Kenny Wheaton's gonna score! Kenny Wheaton is gonna score! 20, the 10, Touchdown! Kenny Wheaton on the interception, the most incredible finish to the football game!" www.eatmyassbeavernation.com
Originally posted by JaguarOn that note, this really isn't the time to decide. It's much better to decide after the games are actually released.
Released and patched ten or fifteen times so that they actually WORK. Never judge a game by pre-release screenshots, demos, or the first few months of release (or, as I like to think of it, the final stages of beta testing.)
Kansas-born and deeply ashamed The last living La Parka Marka
"They that can give up essential liberty to gain a little temporary safety deserve neither liberty nor safety." - Benjamin Franklin
To me Half-Life and subsequently, Counter-Strike, had one major thing going for them--it just felt right. It's almost a smoothness to the engine and the way the game mechanics work. Whenever I play Quake(s) it feels like I'm randomly shooting my weapon hoping to get a hit. With HL you take aim and fire and boom (hopefully) he's dead.
Ok so I didn't exactly compare it with Doom but you get my point. Half Life has always had that something special that makes it better to play.