The accordian has the big advantages that no tuning is needed and that if you squeeze and play a note, you are guaranteed to get a clean sound. At the other extreme, it could take you ages to stop a fiddle sounding like a strangled cat.

At the end of the day, I don't think there is such thing as an easy instrument, at least not if you aim to play well and get the most out of your instrument (not that I can). Some people perhaps have more aptitude to one type of instrument than another and some people may have more natural ability than others but the best players still put in a lot of hard work.