In both cases, you work in Javascript to write your representations, not HTML. Thus, both require some overclocking time to become familiar with a specific API and workflow.
However, I found that titanium architecture is better suited for rapid development. Sencha Touch seems to have a lot more overhead when it comes to building a basic application. In general, I think that titanium is easier to learn.
This is a rather subjective question, maybe not the most suitable for StackOverflow, but there you go.
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