Trying to figure out (if it's not too late) which is better when penning a work involving 1st and 3rd person characters. Protagonist as 1st person and Antagonist as 3rd person or vice versa? Personally, I like me and the readers exploring the sinister mind of an antagonist which I think the 1st person POV does a good job of. As a reader does it really matter how a character is presented to you?
I think you've answered your own question: "I like me and the readers exploring the sinister mind of an antagonist "
I've seen both done effectively, so it'll depend on how well you write it. You might try writing snippets of both and posting them in the workshop when you're qualified.
So you'll include both POVs in the novel, and the antagonist would be written in first person while the protagonist is written in third? How have you decided who's the protagonist and the antagonist? I get the feeling you might be using the terms as synonyms for "good guy" and "bad guy", but I don't think that's a good usage, especially not in this case. If your bad guy is the character you're most interested in and want to explore most deeply, it sounds like he's your protagonist, to me. I assume he has his own goals and motivations, and the "good guy" tries to stop him from achieving those goals? It seems very strange to me to use first person for the antagonist and third person for the protagonist. But everyone is the protagonist of their own story. So if you switch the labels (and possibly the focus) around so that the more interesting character is the protagonist, I think it should work. Does that make any sense? Have I completely misunderstood your issue?
Personally, I despise the use of first and third for different characters in one story. I've seen it done a million times in the YA books I've read, and it infuriates me. When the story is in first person, I'm connected to the story. I'm inside the character's head. But then it switches to third to focus on a different charter, and I find that incredibly jarring. It's hard for me to get back into the story once the switch has been made, so I often lose interest after that. I'd personally just stick with either first or third, not both.