I find a good ajax app to be far more usable than the other two.<p>Every time I start using Flash or Flex I run into annoying issues. The last one was that Firefox has a bug where it says "transferring data from yoursite.com" forever if your flash object does any network activity. Even after the network activity stops. The status bar doesn't return to normal again until a fresh page w/o flash network activity is loaded.<p>I have used a few 100% flash/flex apps and they are pretty annoying.<p>Even websites or blogs that load multiple youtube windows tend to crash Firefox way too frequently.<p>So I'm rooting for html/ajax.