They both cannot be trusted completely . User ratings cannot be trusted because most users are stupid and childish (see DOTA 2 and the like), Critic ratings can be unreliable due to people being paid to give good reviews, but most reviewers tend to actually have integrity. Just because you dislike Civ: Beyond Earth and some users dislike it as well does not mean it is a bad game. Also, using metacritic to judge games is a very bad way of deciding whether a game is good. Here is a great article about that:
Generally, I still find the critics’ reviews (not their ratings, but their actual reviews and their opinion about the game) to be a lot more useful than user ratings, as the average metacritic user seems to be a complete idiot.