This is a personal preference and it could also depend on how you're serving or using the canned tuna. Tuna in oil can add a slightly different flavor and more calories. Tuna in water could reduce the calories and help capture the true tuna flavor. The texture of tuna with oil is something to think about, compared to water as well. As far as blending canned tuna with other ingredients, oily tuna can blend well with the other creamy ingredients too.