Wizards by far.
Everyone keeps saying that the wizard needs to know what he is up against, which clearly does help. But the sorcerer may or may not be effective whether he knows what he is up against or not. If the sorcerer doesn't have the proper spells for a situation, he never will: No leaving slots open to prepare what you need, no coming back the next day with the proper spells, no scouting/magically investigating an area or situation to determine what will be most useful.
Both run the risk of having poor spell choices for a given situation. But if the sorcerer has lousy spells for a situation, he always will.
And your sorcerer will never have the breadth of spells necessary to overcome non-combat situations. I suspect that the majority of replies voting sorcerer more powerful will go on to talk about how they are so great at blowing stuff up or dealing damage in some way. But if your game is structured in such a way the the most interesting option for an arcanist is hurting things then I am glad I am not playing in it.