@nidalpres You cannot compare a M0 core with a M4 one. In order to be fair you should check the NXP M4 family:
http://www.mouser.mx/Search/Refine.aspx?Keyword=nxp+lpc+m4
When I saw that the SAMG55 had good reputation I took a look at it, but the fact that the programming tools are not available in Linux, makes me to keep showing my love for NXP's products.
I'll take a look also to the zeeduino platform. I started to write mine (with compatibility with Arduino's API) but soon I quit the task. The Arduino's API is awful and inconsistent, so it's not worthy the effort to write code base in an API not well engineered. However, no matter how horrible the API is, it's being used for millions, so everything that wants to receive a little attention of the masses needs to be compatible with Arduino.