-HTML5 for cross-compatibility across platforms. Use Phonegap, jQuery Mobile, Titanium, TideSDK as examples. -HTML5 if future web interface. -Mobile app if you will have features relying on system behaviour (ex, iOS iCloud, Android Play Store, etc.) -Mobile app if users need performance, or if they might be using it offline (but HTML5 offline is still an option) But we are now starting to see a hybrid of these two approaches (ex. http://www.orubase.com/ Orubase). It really depends on the requirements, and the ability of developers (cost estimates) to do this.