You should use what feels good to you now. As you gain experience, you might stick with the same rod action, or you might change your mind and try a different one. Most guys who take up fly fishing and stick with it, end up with a closet full of fly rods. Not because there is anything wrong with most of those rods. It's just that tastes change, new models come out, and like women buying more shoes I suppose, we guys like to buy more fly rods because it gives us pleasure and a measure of satisfaction.

My personal preference is for medium action rods along the mid-flex line. I think really stiff, fast action rods are better suited to service as fireplace pokers, but the tips keep melting. Fast action graphite fly rods seem to be correlated to a higher incidence of guys who develop shoulder or elbow issues from casting, and often cannot fish (cast) a full day. Although that's mainly due to deficient casting technique, in truth most people are not expert fly casters. Decent, but imperfect, technique coupled with a medium action rod allows most casters to fish from can't see in the morning 'til can't see at night without developing any physical problems.

Sincerely,

Salmo g.