If we talk about just the money that the group generated for SM, it's probably Exo. It's not just that they had better sales/touring numbers but also they peaked during the 3rd gen when the market was in general bigger and easier to make money. I think SNSD made more money with CFs in Korea but I still don't think it's enough to make up for the crazy amount of money big bgs fandoms can make.
However if we talk about "indirect" money I think SNSD wins. Some people have already mentioned SNSD had more impact but that doesn't translate directly into money. While I agree I think if we want to analyze the situation properly that's too simple. SNSD had a huge impact in Kpop being the top act for a long time, and the impact that had on SM's brand was also huge, making the debuts of the upcoming groups more anticipated and being acknowledged as the top company of Kpop for a long time (also thanks to other groups like SJ or SHINee ofc, but SNSD was the "face" without any doubt), actually EXO themselves and their super fast success were a consequence of SM's status those years.
Might be me but I tend to value this impact more than direct moneymaking, but I understand there will be many people that disagree.
This is a good analysis.
Exo debuted at the same time social media started being a serious thing. It actually affected their growth because SM hadn't known how to use it to promote their idols better and that's how BTS dominated the scene shortly after investing time and resources in the use of social media. So, it wasn't easy for Exo. I remember Exo holding the record for the most watched music video in 24hrs with only 4 million views. Exol also didn't know what to do and they never caught up.
Both ded by 