Depends on what features you want to build.
If you do need access to the phone's native APIs, you WILL need to make a native app.
HTML5 works great for first versions and specifically if everything can be done over back-end API.
HTML5 first, Native later.
To make available more seamless "native" experience to the user.
HTML5 first, Native later. To make available more seamless "native" experience to the user.