Check your location settings. After I installed all my apps on the watch I noticed that many of them changed my location settings for GPS use on the phone. I switched them and noticed better performance. I'd also suggest turning off vibration on the phone if your using the watch as the Haptic feedback should provide that for you. It's not a huge battery drain on the phone unless you receive a lot of emails and notifications, but every little bit helps.
In regards to the Pebble, I had one previously and the battery drain from the Pebble was far worse than watch the Apple Watch does, at least in my experience. However, the trade off I've found is the Apple Watch, even at V1.0 is more seamless than the Pebble ever was. The Pebble would crash at a minimum of 3-4 times per day (and this is even with replacement Pebbles as a result of the crashing).
I think we will see improvements once V1.1 comes, I'd give it a few weeks as Support gets an idea what bugs us early adopters are discovering.