It seems to me like Photon is 'winning' on the price front and ease of programming and of course the cheap wifi connection.
I realize the cloud portion (even the local cloud server) could be considered a disadvantage, but what about things like ability to drive dc/stepper motors or some exotic sensor? Perhaps not enough analog and/or digital pins? etc..
One disadvantage I can think of is the lack of resources whereas the Arduino has a ton of references online with working with all kinds of motors and sensors.