Sup LS. Preferences in music, setting, and graphics aside: My vote is for Metroid (the 2d games in particular) all day everyday. I love all games in the non-Prime 2d series and Metroid II was also one of my preferred Metroid games due to the enemies being more aggressive on average (thanks to the introduction of the constant Metroid life-cycle boss battles) in that title rather than passively patrolling their set/targeting routes like Metroid 1 or Super Metroid.
Since Metroid lacks the rpg mechanics used in Castlevania:SotN and the other metroidvania Castevania titles, that just leaves the 2d Metroid games with maze running and route discovery at their core with boss battles breaking up the exploration. Thanks to the ability to level up, use items, and use magic, the metroidvania castlevania games tend to feel easier as players progress through the game. It can be fun to one-shot enemies when backtracking through areas where the enemies previously took many hits and a strategic approach to take down, but the lessening challenge outside of the boss battles gets to me sometimes. I enjoy this difference in approach between the two series but it makes sense that not everyone loves both series.
With that said, I just can’t get into any of the modern day metroidvania clones that indie studios keep releasing. Something always feels off to me about them like the control responsiveness, hit detection, etc. They aren’t bad games but none of them have captured me in the way that Metroid and Castlevania have. This hasn’t stopped me from trying them out and giving them a chance though. The only non-castlevania metroidvania-style game that became one of my favorites is Oboro Muramasa from Vanillaware. The exploration and rpg mechanics coupled with fast-paced combat made that game something truly special imho.