How is Bus travel in Spain (Madrid)

Hi,

I am planning to book a trip to Barcelona by bus. I saw there is a bus company Alsa. Does some one about over night journey in Alsa? Is that comfortable and Safe?

I checked out the fare difference between fast trains (AVE) and bus. AVE is at least 4 times expensive than bus. Of course it takes only 1/3 of the journey time.

Any way I have to evaluate between tired overnight journey versus expensive and fast AVE.

-Krishna