12 million people watched the debate, for a 54% share, down 5 points and 1 million from the last Zapatero/Rajoy debate (which was, however, the most watched debate in Spanish democratic history). Many polls, apparently, as reported here. But pay attention, that some of these "polls" seem to be online voluntary votes. The ones below are those I could establish actually used randomly selected samples. So who won?
1. El Pais/Metroscopia, N=501, Phone. Rajoy: 46%; Rubalcaba: 41%.
2. Antena 3 and Onda Cero/TNS, N=?, Phone. Rajoy: 43.9%; Rubalcaba: 33.1%.
3. El Mundo/Sigma Dos, N=?, Phone. Rajoy: 51.4%; Rubalcaba: 44.2%.
4. La Sexta/Invymark, N=1100, Phone. Rajoy: 48.6%; Rubalcaba: 39.9%.
Little doubts here, although one might argue that Rubalcaba did less badly than one would expect from current voting intentions. Don't forget, however, that these are self-selected samples too in a way, in this case, of those voters who watched the debate in whole or in part. And these "flash" polls take place very quickly after the debate, which makes fieldwork difficult and is certainly associated with low contact and response rates, with what that implies for sample quality. And that the effects of debates are thought to be relatively small. Etc.
BTW, Publico.es has a nice Twittometer.