What are the advantages/disadvantages of 3/4 time and of 4/4 time?

Apart from the obvious (no one would write a song called 'The Last Waltz' in 4/4!), is each of these time signatures better suited to certain types of songs and tunes?

And if you write your own songs or tunes ... do you start off with a time signature in mind, or does it just evolve along with the song?