I am entering mobile development. I have been working primarily in .NET since 1.0 came out in beta. Before that, I was mostly a C++ and Delphi guy and still dabble in C++ from time to time. I do web apps quite a bit so I am reasonably proficient with Javascript, JQuery and CSS. I have also done a few Java applications. I started web programming with CGI and live mostly in the ASP.NET MVC world these days.

I am trying to decide on which platform/OS and tool to select. I am concerned with the size of the market available for my applications as well as the marketibility of the skills I will pick up.

The apps I have in mind would work on both phones and pads. Some aspects of what I have in mind will play better on the bigger screens that will be available on pads.

Here are the options I am considering:

1. Apple iPhone/iPad using pure Apple SDK (Objective-C)
2. Apple iPhone/iPad using Mono Touch (C#)
3. Android using pure Android SDK (Java)
4. Multiple platforms using something like Titanium to generate native apps from web technologies (HTML, CSS and Javascript)
5. Multiple platforms using HTML5 web applications that run in the browser (HTML, CSS and Javascript).

Which option would you choose? Do you have a different suggestion? What are the pros and cons?