Hello!
I never used the bus but the train or car, indeed the car route is scenic so I can only recommend it but the train route also is...I like train trips though.
Your friends are right, Ronda is a MUST visit place, you will not regret.
About other recommendations, I would not miss a visit to Mijas Pueblo...and talking about Ronda area I know you are choosing between bus or train but for others who will read this, if anyone is
hiring a car I recommend to explore the surrounding area and visiting other villages like Ardales or El Chorro.
For more ideas I just wrote a blog post yesterday about ten places not to miss when visiting Malaga (Ronda is there), just need to translate it to English, will add the link here when finished.
Related post:
http://www.malagaweb.com/forum/viewtopic.php?t=772