1) Slackware 10 has worked well for me. Understand however, that beliefs about distros are almost like religous arguments. Everyone has an opinion, and most are equally valid (or invalid), depending on your point of view.
2) As has been often said in the past,
there is no one best wireless card.
- Define your tasks.
- Determine what software will accompish those tasks.
- Purchase the card(s) depending which cards will work with the software packages.
Most of us carry at least three of four cards at a minimum. Personally, I carry a lot more.