It depends on the game, but to be honest, Flash is a way to go IMHO. Browsers will always provide rendering. HTML 5 is more of a noise thing, and it's a driving force if you want to have iPhone and iPad support. Many other Social Game companies simply transfer their successful names to their native apps if they make a lot of money.
1) What platform makes sense to build a game on facebook, taking into account future market trends?
There is no alternative to Rich Media for Flash. For any challenging game, Flash is the only way to go. As for the back, it is very subjective. Ruby, Python, C #, Php are all common in the social gaming industry.
2) On which platform are there more inherent elements that help prevent fraud? (e.g. flash is compiled in .swf vs javascript as plain text)
Cheating extends to any social gaming platform. Flash can be completely decompiled, so your security should always be handled on the server side. Flash and HTML 5 will have the same anti-fraud solution: server-side validation of everything.
3) Which platform would be the most attractive for the best talent for developing the game for future employees?
Personally, fighting HTML 5 visual addictions is a huge pain. Flash has a problem, but all this is a breeze, and you are fighting the Rendering Speeds and pushing the Flash Player to it.
4) Which platform is the easiest to use in one game and use it for other future games? (e.g. development of isometric graphics in flash memory)
outbreaks. But I would not be ahead of myself. Make one funny name, and then take care of moving it. Porting games from the Internet to the mobile platform is not a 1: 1 port, you need to rethink the interface and someday the game itself. Ideally, you just don’t need to recode the game logic on the server.
5) Which platform is the easiest to develop with a team?
Also.