HTML5
If you want to build a Web-fronted app for mobile devices, the one near-certainty is HTML5. The eventual standard will make various data types simple to insert, rationalize input parameters, level the browser playing field, account for different screen sizes, and probably freshen your breath and give you lush, manageable hair. Eventually.
The problem is that HTML5 is still a proposed standard that is currently supported in a lot of different ways by a lot of different browsers. It’s certainly possible to write HTML5 Web pages now, and many people are doing just that. They just have to know that there might be slight tweaks in the language in months to come and more substantial changes in the way browsers handle HTML5.
From a cost and efficiency standpoint HTML5 has the advantage of building on the current version of HTML so the learning curve is much shallower than that for a completely new language. If you can cope with a bit of uncertainty and want to walk the browser-based path, HTML5 is an obvious choice for a primary language