Your comments

Reading the discussion, I might be wrong. Can you please enable the "Debug Log" setting in the connection's settings, try to connect again and send the log file to support@textasticapp.com?

Thanks!
That usually means that the SSH server doesn't have SFTP configured. Textastic does need the SFTP subsystem to transfer files.
The point is that the iPhone is always in your pocket while the iPad is not. So if the only thing you have with you is an iPhone and your boss calls you to fix an issue on the website: with an iPhone version you could.
I know that it's not perfect. Many people wanted it so I added it. Firebug Lite is loaded from the Firebug website, so it will always use the latest version. I hope they make it more touch-friendly.
I don't know if you have used GitHub before, but you can fork the project on GitHub and work on your own copy. You can also view all forks and see what other users work on. If you have modified an existing file or created a new one that you think is ready, you can send me a pull request so that I can add it to the main repository.

I'm also relatively new to GitHub, but maybe we could use GitHub "Issues" manage that.
Please use the GitHub repo I mentioned above.
You can already create custom code completion files and use them in Textastic.

Yesterday I published the current code completion files as a GitHub repository: https://github.com/blach/Textastic-Customization

The file format isn't documented yet, but it should be easy to understand from the examples. They are simple JSON files.

I'll happily accept pull requests if you are other users create code completion files for their favorite languages.
Thanks, Fexxel. I was going to write more or less the same :)
That still doesn't solve the problem that you can't move the cursor up or down when the code completion list is shown, does it? 

Or do you mean that it would not be possible to choose a different entry than the first one in the list using the keyboard arrow keys? That could indeed be an option - not ideal but better than now for keyboard users. Just hit "tab" to accept the top-most entry and tap with your finger on the screen if you need select a different one.
Yes, MEL as in Maya Embedded Language is supported. Try to choose the correct syntax definition in the File Properties popover. It seems to use the same "as" file extension as ActionScript, so you'll have to select the syntax definition manually the first time.

If the correct character encoding is not detected automatically, you can choose a character encoding by tapping-and-holding the file and choosing "Open with Encoding".