I'd say play what you want. The only consideration is this:
http://dragonsdogma.wiki.fextralife.com/stat+growths
Your first 100 levels are where you get the majority of your stats. If you play a bit of everything getting to 100 you turn into a generalist, not excelling at any one thing but being capable in all areas. If you play strength classes (Assassin, Warrior, Fighter, Ranger) you'll turn into a physical powerhouse. If you play magic classes (Mage, Sorcerer) you turn into Gandalf.
So if you want to be completely OP endgame: pick a side of the fence (strength or magic) and focus on that.
For the record, I went the generalist route (leveled almost exclusively as a Strider) and it worked out fine.