There's a bit of a difference. In 1), you are telling someone what YOU would rather do. In 2), you are suggesting something that ANOTHER person should probably do. You know more information about something and you are saying what you would do IF you were going to do it.
1) I'd rather walk than take a bus. (I am the one who will be walking)
Because I want to get some exercise.
Because I think the bus will take too long.
2) I'd walk rather than take a bus. (If I was going (but maybe I'm not), I would walk)
You should walk rather than take a bus because the bus will take too long.
I've done this before and I know that walking is better than taking the bus, so I would suggest that you walk.