It is not only question of file format. Another crucial question is what exactly you want to store? Is it:
store whole page as it is with all referenced resources - images,
CSS and javascript?
to capture page as it was rendered at some point in time; a static
image of some rendered state of web page DOM?
Most current "save page as" functionality in browser, be it to MAF or MHTML or file+dir, attempts the first way. This is ultimately flawed approach.
Don't forget web pages there days are rather local applications then a static document you can easily store. Potential issues:
one page is in fact several pages build dynamically by JS, user interaction is needed
to get it to desired state
AJAX applications can do remote communication with remote service rendering it
unusable for offline view.
Hidden links in javascript code. Such resource is then not part of stored page.
Even parsing JS code may not discover them. You need to run the code.
Even position of basic html elements may be recomputed may be computed dynamically by
JS and it is not always possible/easy to recreate it locally.
You would need some sort of JS memory dump and load this to get page to desired state
you hoped to store
And many many more issues...
Check Chrome SingleFile extension. It stores a web page to one html file with images inlined using already mentioned data URIs. I haven't tested it much so I cannot say how well it handles "volatile" ajax pages.
