Can I choose whether hobbyist or Part 107 rules are more advantageous when flying a UAV for fun? According to the FAA's UAS getting started page, if I'm flying a drone for fun within a 5 statute mile radius of an airport, I need to contact the airport and any air traffic control tower before flying. As a Part 107 pilot, I can fly a drone in class G airspace up to 400 ft AGL (or over a structure) without having to contact anyone.

I have a current Part 107 remote pilot license. To me, this makes my ability to fly a drone more flexible.


If I want to fly for fun within 5 miles of an airport and the airspace is class G, I can decide I'm flying as a Part 107 remote pilot and then I don't have to contact ATC or the airport.
If I want to fly for fun within a surface non-class-G area, I can decide that I'm a flying as a hobbyist and contact ATC and the airport if I'm within the 5-mile airport radius, no airspace authorization necessary. This is a no-go if ATC says no, but otherwise a lot faster than applying to the FAA for a waiver to fly in controlled airspace.


In either case, I would ensure that I'm not anywhere near other air traffic, and that I fly safely.

When I'm flying for fun, can I pick and choose as to whether I fly as a hobbyist or a Part 107 pilot?
According to the FAA's own FAQ, you can do either (emphasis mine):


  There are two ways for recreational or hobby UAS fliers to operate in
  the National Airspace System in accordance with the law and/or FAA
  regulations. Each of the two options has specific requirements that
  the UAS operator must follow. The decision as to which option to
  follow is up to the individual operator. 
  
  Option #1. Fly in accordance with the Special Rule for Model Aircraft
  (Public Law 112-95 Section 336). Under this rule, operators must:
  
  [...]
  
  Option #2. Fly in accordance with the FAA's Small UAS Rule (Part 107).
  This requires operators to:
  
  [...]


So, it's your decision. But as always, ask yourself first how you would justify that decision to the FAA if something goes wrong. As a certificated pilot, you actually have something to lose if the FAA decides to take action against you.