Hi John,
Thank you for the inquiry. The answer to this question really depends on where and how you plan on fishing the rod. Longer rods tend to be better for three things; long casts off of beaches, roll casting and using a nymphing/high sticking technique. A 9' rod tends to be the most popular size because of its versatility. If you are looking for a rod that will chuck the bigger streamers that have become popular in the last 10 years, you may consider looking at a 9' 9wt matched with Rio's Big Nasty. This rod rules the roost when it comes to casting the likes of the Dolly Llama and other "Big Nasty" flies.
I hope that this is helpful.
Best Regards,
Mike Cole
Alaska Fly Fishing Goods