Yoigo is excellent
 

I always buy a Carrefour SIM when visiting Spain, but when I arrived this time I found out that they changed the service around and you only refill your data allowance once per month.

I asked around at several other phone shops and I was told that the situations there were the same for prepaid except with Happy Móvil.

I bought that SIM but it was pathetically slow. Then I heard that Yoigo allowed unlimited refills so I bought that SIM at a Yoigo shop and it has been awesome in every way.

Also the help I received at Yoigo was extremely knowledgeable which was a breath of fresh air.

You can see the taxes here: http://www.tarifasyoigo.org/tarifas-movil-tarjetas.php