It's pretty hard to say which character is easiest to get to 250. Different characters excel in different parts of the game with different levels of funding.
If you want a decent BoF, F/P mages are great. Early levels are solid with low funding and you can level past 3rd job super fast with poison training. This generally requires having your own Bishop though. You can get to 150-160 in a couple days like this. It slows down though since it's hard to boss and HoH though.
I highly recommend just playing another class you think you'll enjoy as a second character.