St. Louis has the better scoring finishes near the top, but outside of '04 which was the best season by either player, all his top seasons came next to a high scoring center while getting big offensive minutes on a weak defensive team. He was good defensively early in his career and a shorthanded threat, but I think he largely sacrificed defense for offense after the lockout and his underlying numbers weren't good.
Hossa meanwhile only really got to play heavy offensive minutes for a bad team in Atlanta. In Ottawa, Detroit and Chicago, he always played under 20 min and always remained a good defensive player. St.Louis was over 20 min his entire best 10 year period.
Even still, as Trent McCleary shows above, their 10 best years aren't that far apart offensively. I was ready to say that the numbers undersold St.Louis when looking at league scoring, but they stay roughly the same even if we look at their scoring relative to the 10th scorer each year. And Hossa has several more years outside of that period where he was still very good.
St. Louis looks better on paper when you look at finishes and awards, but overall, Hossa was the better player. I mean, St.Louis was clearly never seen at the level of player his scoring numbers suggest while he was playing, it's strange that he seems to be held in higher regard after the fact because of them.