Which Chipset should I choose?

I want to buy a new motherboard, but there are some obscures informations and topics about chipset that create doubts. For example: which chipset would be the best for P4 or Athlon? (don´t mind which socket). Last month I could buy a motherboard with a determined chipset and today it is not up-to-date. Which criterions should I take as important to get a new motherboard and choose the correct chipset? Is the chipset responsible for a good performance? The chipset could be responsible for some kind of compatibility between some component ?
I am asking for orientation because I really could not find a specific text about chipset. Somebody can help me? Sorry for my inexperienced.

Marks

For AMD I'd go for a nforce 4 ultra, or if not at least a nforce 4. And for upgradeability socket 939 because with a bios update you can upgrade it to a double core Athlon 64.

If there is a possibility of several things going wrong, the one thath will go wrong first will be the one that will do the most possible damage