Pure HTML 5
Each of them has pros and cons and you can find many comparative tables on the Web.
The main reason we are going to create a hybrid application instead of a pure HTML 5 application is that we want to access device features (such as contacts and calendars) and we cannot do it with a pure HTML 5 mobile application.
You can search for hybrid mobile application on Google to get all the explanation you need; I'll not cover more here because it's really out of topic.
If you are a BackboneJS developer you should choose Titanium, because they integrate really well using Alloy.
Otherwise you should go to PhoneGap.
There are many different popular frameworks used with PhoneGap...