There is not such thing as a "best" longboard brand. It is all personal opinion, but there are better brands than others.
Sector 9 and Gravity are okay beginner boards.
Sector 9's are widely available, but their quality is not that great.
Gravity's quality is nicer than Sector 9.
Originals are flexy boards with a unique truck system. Orignal's trucks require a lot of maintenance and cannot be taken to higher speeds, so much of the longboarding community does not like Originals.
I would recommend looking at brands such as Earthwing, Landyacthz, Comet, Bombsquad, Jet, Rayne, and Never Summer.
Sites like these will give you a better idea of what good brands are out there:
http://www.muirskate.com/
http://motionboardshop.com/
http://socalskateshop.com/
http://longboardskater.com/
http://www.daddiesboardshop.com/