Having done the Airport Rail Link in both directions twice and having done both the Express and the local City Line, I would say its a quick and easy way to Nana, but I would recommend taking the local City Line all the way to Phaya Thai and switching to the Sukhumvit line there, which will make the trip a shade longer, but will require only the one switch, and you can travel all the way to Nana. The only time I do not advise this, is if you are travelling with a lot/heavy luggage since you have to navigate steps during the switch. Good luck..