"The most successful console systems of all time in terms of total hardware unit sales were the Sony PlayStation 2 and the Nintendo Wii, says DFC analyst David Cole. "The PS2 and Wii also had the record for largest initial launch sales but the PlayStation 4 surpassed both those systems."
However in further analysis (subscription required) DFC state that they don't think PS4 will reach the record levels of Wii and PlayStation 2 in the end.
Other analyst are of a differing opinion (Baird Equity Research via MCV) claiming it's a dead heat and that Sony and Microsoft will be going at it neck and neck.
Either way the next-gen race has just started and while some analyst may be eager to call a winner at this point (it's their job to do so after all) nothing is certain at this point.