Can you play Unreal Gold or Unreal 2 with a gamepad? Also, which one is better?

You can play with a pad, although I don't really recommend it. FPS games such as this require the precision aiming capabilities of the mouse and the quick movement of the keyboard.
As for which game is better, I think Unreal Gold is loads better. Haven't played the second one, but I heard it was a huge disappointment was probably the main reason Epic doesn't make any more single player Unreal games.

Unreal 2 isn't a true sequel to the original Unreal. It was developed by Legend Entertainment, rather than Epic, and it is very different from the first, with a stand-alone story. It's also more of a standard story-driven FPS than the original Unreal, which was far more atmospheric and gave you the impression that it was much more open and free than it really was. There's a lot of yakking in Unreal 2, unlike the more quiet original, where you discover more about the planet (etc.) via texts transmitted via your universal translator.
I played through and finished Unreal 2 in a short amount of time. It looks pretty, but I never really liked any of the characters, and the story was plodding. The weapons were unsatisfying to use and movement felt clunky. So if you're looking for a good single player experience, I would recommend the original Unreal.
Mutliplayer Unreal 2 is quite a different beast. You get the option of installing either Unreal 2 singleplayer or the Extended Multiplayer version (XMP) when you buy it off GOG. XMP is multiplayer focused, and I don't think (though I can't recall for sure) that it supports bots. I found it a bit too muddy for my taste, but others swear by it. There is, however, a much improved version of XMP available for Unreal Tournament 2004, so even in that case, Unreal 2 isn't necessary. (And I would recommend other games if you were looking for a good multiplayer game, anyway.)
So in short, if I were to pick one or the other, I would go for Unreal Gold.
Edit: and I certainly wouldn't recommend using a gamepad, either.