>>15457117
Play them in order of release so you can experience the gameplay changes and improvements of each title.
If you play a newer one and go back to play an older one, you might find the older boring/bad simply because of the downgrade, when in fact they are all pretty much good games on their own.
Play the Classicvanias first, up until Rondo of Blood. Then, play the Igavanias.
If you want different experiences from both styles, play the PS2 and N64 titles after that.
Except for Castlevania 2. That one is tedious even with patches.