Personally I liked DoS's Julius mode the most, by far. While every other mode just felt like "ur playin' an uber-fast d00d and keel everythin'", this one had a certain depth to it. Just the bare fact that you could actually choose from three styles of play really added a lot to the overall experience. Oh, and Soma Dracula was really neat, along with one of the best versions of Dance of Illusions. That hint of storyline did wonders to the story, and the material given was way better than anything else in the game
Other than that...Maxim and AoS Julius mode were actually a lot of fun, so they get second place. Not sure which one, though, they were both really good in their own ways, but I can't really decide between the two. So I just entered DoS Julius mode, didn't vote a second.
In regards to SotN's richter mode...I felt that it really didn't fit the style of the game, resulting in an overall "meh" experience. That, and Richter just controlled really, really weird, being more agile than in the old CV games but not nearly as flexible as Alucard. Not something I'm terribly interested in.