Finding the right fly reel can be challenging with so many options out there. Focusing on a few key factors will narrow the search. For instance, start by asking how much capacity you need for the application. Then, you can think about overall weight of the reel to make sure it balances well with the rest of your outfit. Finally, more technical questions like drag style and performance should be answered. With that information, you'll still have a nice range of fly reel options available to you.
Investing in a good rod is one thing, but I like to invest in a good fly reel as well. A simple click/pawl reel is fun for small streams and schoolie harbor fishing but there's a lot to be said for a good cork or sealed drag system. Look for a reel with a good drag system and plenty of line capacity if you're after hard fighting fish or fish that can take a lot of line.