We use Dia Queen, and it isn't over priced here. Mitsubishi offer a good warranty, but want you to use their products - our Triboligist says they have signifiers in the oil and can check on a warranty claim. That said, Mitsubish and Nissan both have a big stake in Jatco, even before Nissan got a big stake in Mitsi, I can't see the Mitsi stuff being anything special beyond what Jatco needs. Castrol supplies Mitsi engine oils here, but not Dia Queen, so being in Mitsi good books, I'd go for Castrol.