There's no wrong or right way here. The benefit of using a valve is less equipment to clean after brewing, no heavy lifting if you have enough height to gravity drain, and the option of using a kettle screen to help keep hops from going in the fermentor. Of course the screen can get clogged, making it a slow painful draining process.
Using a siphon is easy and other than cleaning, doesn't have many negatives. You can use a reusable muslin bag for filtering as well. The bags can be a headache to clean, though.
Also, as mentioned before, you can always dump it all in a bucket if you don't care as much about the clarity or the hops going into the fermentor. I often do this for stouts, porters, and hefeweizen.