Out of The Witcher 1 and 2, which is the better game? I have heard it both ways, and I'm not sure which to invest in.

Why wouldn't you start with the first one?

Do bear in mind this is but my own personal opinion, and in no way reflects the thoughts of a majority of gamers.

In terms of game play, I'd have to say I very much prefer The Witcher 2. It's more easy to get into, as long as you've played some "contemporary" 3rd person "over the shoulder" action games. That's basically how it plays. If you are one of those gamers offended by the so-called "consolization" of PC games, then I guess you'd feel more comfortable with The Witcher's control scheme, since it caters more towards the old school gamers, and has quite a steep learning curve, when it comes to combat.

Story- and script-wise, I prefer the first game. I love them both, I don't think you can like one of them and hate the other, they're both amazing games, but I slightly like the first Witcher more, because of the story and the writing; it had me a bit more interested and engaged.

So, if you're going for game play alone, I'd definitely say start with The Witcher 2, but I would honestly recommend you to go with the The Witcher, first, since there's actually a continuity between the two games, and, overall, the story of The Witcher is a bit better crafted and provides minor insight and background to the things you do in the second game.

Note that the second game follows directly from the story of the first game. So if you want the whole tale, you'll want to play them in order. I generally agree that the actual play is better in the second game (combat especially), but the first has a more involved and personal story. If forced to chose between the two, I'd probably pick the second as the better game, but it's worth playing both.

An important thing to note is that if you try one game and don't like it, you might still like the other, since they play differently.

I guess it depends on how important story continuity is for you.

Sorry I answered your question with a question, BTW. :)