My two cents or rather $0.004 on the debate as to which is better for marketing your books.
I have found in my limited experience that offering free books on Smashwords is a very successful means of gaining readership and developing name recognition.
As far as sales though, for myself Amazon is leading at 100% and Smashwords 0%.
I could not get Amazon to price match to $0.00 for my free reads so moving forwards I plan to market my free reads on Smashwords and paid reads on Amazon.
Goodreads is an essential component regardless of what marketplace you utilise, for readership and rankings/reviews.
Each author must decide for themselves what’s best for them. I hope this works for me but only time will tell.