As DM, which alignments to you allow (and disallow) from your campaigns?

As a DM, I do not disallow any. But if a persons is going to play a character who is a monster, there will be a price to play. Not even the most corrupt Thieves Guild wants to be associated with a mass murderer.

As a player, what are your favorite alignments?

As a player, I prefer the three chaotic alignments and the three evil alignments. My chaotic characters do not revel in chaos or anarchy, they simply do not like to be told what to do by the oppressive powers to be. As adventurers, restrictive laws usually get in their way.

Similarly, my evil characters are not very evil, and they are not monsters. They are evil because they put their self interest above the common good. What is wrong with that?