I'm new to Fallout, and I'm wondering which one I should go for first? I'm assuming the obvious answer is the first one, but what is Fallout Tactics about? Which of the 3 on gog.com is the best? And do the stories continue, or can I start with any of them?

Fallout Tactics is not really canon. It's supposed to be good ( haven't played it yet...) but it is not real Fallout.
I would start with Fallout 1, otherwise you might get spoiled by the features in FO2. You don't have to go with 1 but it is nice to go in chronological order.
Fallout 2 also has all the fan made mods for it, so I guess judging by the sheer amount of mods, it could be tentatively termed as the "best". YMMV.

i remember after finishing fallout 1 and enjoyed it a lot, i was really eager to play fallout 2. in the intro movie i was like: yeah baby that was me, i killed the master!!!
hah good times. wish i never played fallout though. so i could play it again.

I also liked knowing exactly what Tandi was talking about when I met her in NCR.

I liked finding the ruins of Vault 13 ;)
And the amusing quirk of one vault having 50,000 water chips, but no GECK, and then you come to find out Vault 13 had extra GECKs >.>

Or finding a bag filled with 10,000 bottlecaps...in Fallout 2

Fallout 1 is the best IMHO. 2 is great as well, but clearly unfinished. Besides, the beginning of 2 spoils the end of 1 so play 1 first.

this topic spoils Fallout 1 too =/

Well, Tactics is semi-canon. Things in it that do not contradict FO1 and 2 are considered canon by both Bethesda and Interplay.
And yes, start with the first.
Chronologically, Tactics takes place between FO1 and FO2.

Fallout 2 has lots in it that refers to fallout 1. You won't be lost without FO1, but it sure does make FO2 better - so I'd suggest starting with the first (as I did)

I'm guessing they don't use bottlecaps as currency in 2?

Not at all sorry..

lol, Fallout 2 is the best to download, but if you have the computer power, try getting Fallout 3 (i get 3fps on my laptop ^-^)

I'd suggest, if you want the story, to start with Fallout, then go to Fallout 2, then if you have it Fallout 3, anywhere between the end of 1 and whenever you could play tactics as it does not relate to the story.

Start with Fallout 1, then Fallout 2, and then Faloout 3+DLC!
Yes, I'm boring. :)
Fallout 3 was my first Fallout game. The first 4 hours was complete hell. It was WAY over my head, and I basically sucked. Now, I'm at 70 hours and I'm loving the hell out of it!
After I got to Level 20 (which was unfortunatly before I could finidh the game, thanks to a side-quest overdose) I now have to wait until Broken Steel comes out in a few weeks.
So, I got the first Fallout. It was the like the first 4 hours of Fallout 3 all over again. Once again, everything was over my head, and I was REALLY scuking! I'm getting better as I go (I learned how to upgrade my stats after I level up. Thank you God) and I'm already at Level 3.