Traveling to Europe - need SIM cards

Hey guys,

I'm planning a European vacation this late spring, early summer, and am researching on SIM/cell service providers. It's all a bit over my head, as it's my first time traveling overseas and wanting to use my cell phone. My wife and I have the Nexus 4 and 5, respectively, and bought them straight from the Google Play store, so it should be unlocked and ready to go. We are planning on visiting the following countries: UK, France, Italy, and Spain. I'm mainly interested in texting and data, and the occasional phone call every once in a while.

Where would be the best place be to pick up a SIM card? I know I can buy one online and have it shipped to me, but it seems to be more cost effective to buy one when I land in a particular country. Who would be the best service provider to choose from?

While in the UK, it seems like Vodafone's freebee data plan might be the best choice for us. It's cheap, gives us plenty of texting and data allowance, and some credit for making phone calls. Does anyone know of a similar deal for the other countries? Or is it better to get a European SIM card and just use one provider?

The other option would be somehow using Google Voice for texts. I can't figure out if it works overseas or not, but some research says that it may not? We're both on T-Mobile in the US, so I'll have to see how their international roaming plans work with the $30/month plan. as another option. Didn't they also introduce free data as well?

Anyways, hoping to get some help on this and this community has always been great at answering whatever questions I've had in the past.