Dreamcast and Nintendo 64 are my favorites.
Sincerely, there's no motiv to take these how "favorites", is something that comes deep from the heart, but i will try to answer.
Dreamcast is a arcade machine, like your predecessor, the amazing Saturn, unfortunately both was a commercial failure, but, the Dreamcast had some efforts and give us the best of that period with such great fighting, racing and platform games, till the few RPGs like Grandia 2 and Skies of Arcadia are marvelous.
Nintendo 64 is one of biggest suprises in my life, Mario 64 is the last game that really blew my mind, after came other beatiful and memorable 3D platformers like Conkers, Banjo and Goemon series, and the amazing racing games? I love so much Rush 2 and Beetle Adventure Racing.
I adore all videogames in general, but theses two, Genesis and NES, are the most important for my gamer life.