When you have an option to present to the user that has more than two choices, how do you do it?

Do you use horizontally aligned radio buttons:

…or do you use vertically aligned radio buttons:

…or do you use a combo box:

I’m starting to think that combo boxes should always be used. There are easy to add more choices to later on; They save space on a potentially tight dialog; And IMHO there are just cleaner looking than the alternative of cramming all these radio buttons onto one dialog. Plus if you need to change content on the dialog below the choice in question, they keep all the content in close proximity and form a nice logical grouping:

So… how do you decide whether to use radio buttons or combo boxes?