I stayed at Hotel Quo Fierro for 10 nights recently on a business trip to Tres Cantos, Madrid. I had previously stayed in central Madrid for an earlier business trip and found getting a taxi to the office every day such a trial (the majority of taxi drivers in Madrid are not remotely interested in taking you out to Tres Cantos - no more than 25 minutes away - 4 taxis on a single morning refused to take me!) that for my return visit I chose to stay in Tres Cantos instead and walk to work.
This is a modern hotel situated beside the train station in Tres Cantos and there are very regular trains into the main stations in Madrid - Chamartin, Nuevos Ministerios and Atocha. The hotel is also walking distance to the Technology Park in Tres Cantos so from this point of view was very convenient for my needs.
The hotel is clean, reception desk is helpful and friendly with English spoken for non-Spanish speakers, the rooms are sparse but adequate, the bathrooms are nicely equipped with great, powerful showers which do seem hard to find in European hotels and there is a cafeteria/restaurant downstairs where a good buffet breakfast is served (14 euros if not included in the room rate) and you can get dinner most evenings except weekends - however you may be the only diner some evenings no matter how late you leave it before venturing down to eat!
And I guess this is my only hesitation in recommending the hotel - it is so very quiet that sometimes you imagine you must be the only guest!! Where is everyone in the evenings? Why no buzzy atmosphere? Could it be the lack of a real bar other than a counter in the restaurant? Could it be that the centre of Madrid is only 25 minutes away by train? I don't know but if you're a solo traveller you may feel just a little too conspicuous here and the evenings may feel just a little too long and lonely.
Bring lots of English DVDs for your laptop and good books and you may be ok but expect to hear the clink clink of your cutlery on your dinner plate in the evening!! If you don't mind this then I'm sure you will be happy staying here.
A small final note about the hotel's website - I found two different sites offering two different sets of information about availability - one said there were no rooms available on some of my required dates and the other said there was availability. I booked on line and then emailed reception directly to check that my reservation was definitely confirmed. Then I booked a second room on line for a relative who was coming to spend the weekend with me and they had no record of the booking even though I had had the emailed confirmation. Luckily they had rooms as my relative was in reception when they told us they didn't know about the booking! Guess they need to check out the problems with their online booking system.

Good business hotel to visit Madrid. Rooms are well equiped and include free Internet. The buffet breakfast is good. Travel to Madrid by train takes about 20 minutes to connect with the Madrid underground (Nuevos Ministerios). This makes it a good and economic option to visit Madrid. Staff are friendly and speak English.