Have you figured out that asking about a Reel is kind of like asking about a fly tying Vise? Most people's favorite brand is whichever one they own.
As for the original question, I've been using a TFO BVK on an 8 wt primarily on Lake Texoma pretty much since this reel model was introduced. I've been happy with it. I got one for a 5 wt about 2 years ago and I've really liked that reel. It's a nice light weight reel that has worked very well on the lighter rod.
I've never been a situation with either of them to put heavy stress on the drag, so I can't really comment on the durability of the drag if you're planning to take it into saltwater to chase large/fast fish.
I also have a BVK reel on the rod I teach with, and this reel has proven to be very durable to external wear. Instructor rods and reels have a hard life and the BVK has held up well, much better than the reel that was its predecessor.
I have several BVK reels and I like them. They've held up well.
I have never fished the other reel, the Orvis Hydro, so I can't comment about it. I just don't know anything about it.