HTML5 IS NOT yet ready.
HTML5 IS NOT yet stable.
HTML5 IS NOT yet supported universally.
HTML5 IS NOT yet able to make many things which are made in Flash.
HTML5 IS NOT yet nearly as convenient as Flash is for gamedev.
A such HTML5 game that is considered a big achievement to develop is done in Flash in a few days.
Also, good Flash and AIR games are published via Steam and such now and then because of their ‘console level’ quality.
…and HTML5 games are starting to show up on Kongregate because they are of similar quality to their Flash brethren… Do you believe that HTML5 will not make the jump to the console in the next few years? It seems inevitable, in my eyes. Particularly for the Playstation and Wii consoles considering that they already have integrated standards-based web-browsers. As you can already purchase HTML5 games for the PC from a number of vendors, I’m sure it won’t be too long before Steam picks up support for them as well.
HTML5 is not yet suited for gamedev. It CANNOT be considered a Flash replacement. You CANNOT make games in it. Period.
If the question is straightforward “Where should I make browser games now, in Flash or in HTML5?”, then the answer is short: “In Flash”. You cannot do it otherwise.