I'd suggest /fopen for writing html before binvars-- firstly because it would be simpler to manipulate than a binvar but moreso because whatever ends up using it won't have to reparse the data 4096 bytes at a time through a binvar loop. Also it would ease the debugging process of being able to view an html file..
It would be interesting to know what in mIRC would be processing this? If it's not meant for mIRC to use, I'd say files for sure-- if it's being passed to some HTML dialog viewer DLL then maybe it's a different story (though any HTML viewer I know can just load up a file from a filesystem real easy).
