To be frank - it really doesn't matter. Just choose a fly reel that you like. Follow your bliss.
It's all down to personal preference. The whole balancing a fly rod on your finger with a certain reel is quite frankly - a load of rubbish.
The forces, inertia and perceived weight on a fly rod in play are dynamic - they vary greatly depending on many factors, primarily the amount of fly line you have out.
Just choose a good reel, one that you dig and you'll be fine. The fly rod doesn't care.