I'm a student of CSW under Erik, so I'll give my opinion, as bias as it may be.
I think the stand-up in CSW is second to none. A blend of MT, Boxing, Jun Fan and Savate - and all of it battle tested. So to answer the question from a stand up point of view, I would say without question - CSW.
From a ground point of view, the only thing I would highlight is that Erik's material is focussed on no-Gi submission, so there is a contrast to BJJ. Therefore it depends on your ultimate goal, and how much emphasis you place on the Gi, before leaving BJJ behind.
If I was given the choice, from an MMA point of view, to train at one gym and one gym alone - I would pick Erik's.
I hear they got some tasty burgers.
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MY GIRL CAN'T KICK OR GRAPPLE, BUT YOU SHOULD SEE HER BOX |