Well, some bots do support granite. But I havent checked up on rsbots if they do support it. I have kminer. And it wouldnt be recommended for a lvl 3 to do granite. I'd say try Varrock mines, or west of fally mines.
I would suggest you do power mining iron, as its the fastest, but coal is okay if you want some decent money. I'd say a month or 2 doing coal. But iron will be quicker.
EDIT: Yeah, granite is fast too.
Willows are the quickest. Yews would probably get you banned faster because everyones whos botting there will be moving at the same time. Willows is safer imo.