Oh, now that is an interesting question.
It is a tossup, really.
Victoria and Baker Street are two very historically accurate Victorian-era RPGs. No steampunk, no gothic horror, no supernatural. Straight-up exploration of one of the more fascinating ages (in my mind) in history. I love my Steampunk. I LOVE my Gothic Horror and Supernatural. But that loves comes from a solid grounding in the age, and these game both managed to give me what I love and be very clever about it.
Likewise, I love the tales of King Arthur and an age of a Mythic Britan.
While less grounded in actual history, these books both capture their subject matter well. Pendragon and Chivalry & Sorcery are great fun, and I just don't get to play them enough.
It is great to do a historically accurate RPG as Victoria and Baker Street show, but Pendragon and C&S also demonstrate why historical accuracy sometimes needs to take a backseat (or passenger seat) to a good game.