Only tabs, never spaces.
The reason for the former is that if someday I get hit in the head and decide that I want 2 column indentations rather than 4 as I'm using now, I don't need to do a global replace; I just need to configure the editor.
The reason for the latter is that many assume that tab will have some predefined width, so it's not unusual to see something like this: --tab--> Some text:
--tab-->--tab-->Some other text.
--tab-->--tab-->Some other text.
Which sometimes looks like this: tab> Some text:
tab>tab>Some other text.
tab>tab>Some other text.
For output indentation, however, I exclusively use spaces.
As for braces, I've always liked (mostly) The One True Brace Style. It's the one I came up with myself (I didn't learn it from the book), so it's the one that feels the most natural to me.