What's the best sim card for using iPhone 5S around Europe?

So I'm going to Europe in a couple of weeks and was wondering what my best option if for using my phone. I'm travelling through Italy, Austria, Czech Republic & France. Additionally, would I require a new sim card in those countries to avoid roaming charges or aren't then any in Europe for european sims?

Also, it's an iPhone 5S so I need a micro sim… Will that pose an issue? Can you buy sim cards at the airport in Rome?

O2 offer certain cheap european deals, I'm on Vodafone which is a rip of. But when travelling there's no cheap way as every country requires another sim.

I use skype and just ring when I'm in hotel or hostel which always have Wi-Fi. You can just use your sim ( contract or credit) as a back up when you can get Wi-Fi.

But when on Wi-Fi both skype and Whatsapp are ideal!