I went through the same debate before settling on the Turbo. The number one separator is battery life. I don't like the feeling of panic when my battery is down to 10% and it's, say, 8:00 o'clock at night and you have to ration the use of your phone. You'll never get that feeling with the Turbo.
I don't like TouchWiz or the back button on the S5. The S5 is loaded with Samsung software, most of it I doubt I'd ever use, but might be fun to play around with. The Turbo has useful software features like Moto Actions and Moto Voice. For example, you can use a custom spoken phrase to wake your phone and perform actions without touching it. I amaze my friends by doing Google searches with the phone in my pocket. "Obey me Droid Turbo" is my custom wake-up phrase.
The S5 supposedly has a better camera, and this was the one feature which almost swayed me. However, I see the same complaints about the camera in both forums--slow shutter and blurry low light photos, so I went with the Turbo. There are more settings on the stock S5 camera than the stock Moto camera, but an aftermarket app can correct that on the Turbo.
The Turbo has got a high quality feel to it. Built like a tank. The S5 seems flimsy and lightweight in the hand. Go to the store pick them up and compare them. You'll be handling your phone for the next two years. What do you want to feel when you pick up your phone?
Motorola has become a leader for pushing out OS updates quickly. Samsung is a known laggard in this area. I'm sure Moto will release Lollipop for the Turbo much sooner than Samsung will for the S5. Lollipop also promises improvements in camera.
Droid Turbo vs. Samsung S5: