Quake II definitely.

Feel like a lot of people will pick Half-Life 1 just because its so well known.  It was a fantastic game in its own right, but if you pit it up across Quake II it's hard to see it coming out on top.  Both are still thrilling games though, and way ahead of their time.

I would buy it... if the PS4 also required a constant internet connection.

However, if the PS4 did not require you to always be online, and the Xbox did, then I'm switching over to Sony.

I've had times where the internet goes down for 3 days, and there's nothing I can do about it.  If I'm offline, there's no reason as to why I shouldn't be able to play single player games- I paid for them, they are mine.

Microsoft probably won't do this though, so likely won't be an issue.  I don't think they're that stupid.

Computer version is better in almost every way but conveniance.  The only place the 360 has the definitve edge is its accessibility. Anyone can pick it up and play it, whereas on the computer you have to have a bit more dedication.  As far as gameplay itself goes, the Xbox version is blown out of the water in almost every way.  That doesn't make it a bad game, it's just that it's hard to compete with one of the most popular games in the world right now.