Jason Mraz is very talented. From the list, I'd say Mason Jennings is the best lyricist. The man is a modern day Bob Dylan "Ankles crossed, hands behind my head, singing songs and telling stories about the weeeessssst." John Mayer is probably the best pure guitarist. The dude can flat out play guitar. I think overall Jack Johnson presents the best combination of songwriting skills, instrument playing skills as well as being a great producer (Donavan Frankenreiter) and being an award winning movie director (September Sessions). Not to mention the guy spends most of his free time playing guitar on the beach in Hawaii and surfing. What a life
But, all the aforementioned artists are very talented and very unique especially when compared to most popular music today.
