I also don't know enough about RENFE, to pass comment. I believe they are Spanish?
Operates the widest variety of high speed trains in Europe - plain fast clones of TGV and ICE plus Talgo/CAF designs of bi-mode, bi-gauge, bi-current, tilting stock.
Tend to like big but infrequent trains, reservation-only, all luggage scanned prior to boarding (long distance) after Madrid terrorist attack.
I've found them rather fussy and inflexible (eg not letting you change seats), but that might just be circumstance.
Pretty useless web site which can't handle connections for through journeys, OK for point to point and some good advance-type fares.
Biggest operator of Talgo and CAF stock (who are both bidding for HS2).
They operate 3 levels of service: long distance, regional (MD) and Cercanias (local/metro), with no easy transition between the levels.
Poor safety record (notably Santiago de Compostela 2013), along with infrastructure operator ADIF.
Four major high speed lines from Madrid (to Seville/Malaga, Valladolid/Leon, Barcelona/Girona/Perpignan, Valencia/Alacant) and still building.
Beginning to think about competition at home, but currently are the monopoly operator (some separate local operations in self-governing regions).
The Spanish government has got a plan for RENFE privatisation, but it hasn't got very far with it.
PS. I should have said that RENFE have major contracts for operating high speed overseas, notably in Saudi Arabia where they are part of the consortium running the Haramain high speed line (with Talgo stock).
They are also active in high speed rail planning in USA and Latin/South America.