So, like, basically, every single character in the game besides the villains are my secondaries, I just favor a few over some others, though it depends on my mood. I'll play both the Belmonts, but I favor Richter because of his design, more endearing personality, and overall just feeling overall lighthearted and more heroic compared to Simon. Ironically, my first Castlevania game was Castlevania 1 on the Wii's Virtual Console, and I've never played Richter's games. I also feel like the overall moveset fits Richter more than Simon, as Richter is more recent in-universe as well and thus has had time to not only master the techniques of his ancestors, but create his own.
That's not to downplay Simon though. I won't deny he's got a lot of appeal to some as a rare embodiment of pure, raw masculinity with only maybe his long hair being any sort of "pretty" in a cast that's mostly comprised of guys who have at least some sort of pretty boy traits, and it's hard to deny how badass it is that Simon only had the Vampire Killer and a few holy weapons when he killed Dracula. Which I know he did at least twice, but did he ever fight Dracula again after Simon's Quest? Like, canonically. I know he's been in a lot more games, but I don't really know the specifics.
Ultimately, I'm really happy they're both in the game, I love how they both echo each other in some regards, and I'm going to enjoy both.