Originally Posted by pcknshvl
Wide? Narrow? What "feels comfortable?"
Assuming you are talking about Spey casting with a two-handed rod vs. overhead casting, I teach the wide grip for specific reasons...
Since Spey casting is much more than just the forward cast, most will find it easier to lift, set the d-loop and otherwise manipulate the line to prepare for the final forward cast. The load on the top hand will be lighter in general, and less power needs to be applied from the bottom hand.
In my class I emphasize that "the body accomodates the arms, the arms do not accomodate the body". This is less true for underhand / short head styles but is a key concept for general Spey casting and a good learner's rule. A wide grip encourages the student to properly rotate the hips and move the whole body through the motions leading up to the power stroke of the final cast. This is very important to establish.
Beyond the initial learning curve there are many factors affecting the choice of grip style including the length of the rod, the design of the line, even the casting technique but in general when starting out I highly recommend the wider hand placement to establish good Spey technique.
Once you've examined the effects for yourself the answer becomes "whatever works for you" as it's a subjective thing in the end.