I have played through CV64 more than LoD due to owning the former and having only beaten the latter's main quest on a rental. But I think CV64 should be played first. It actually has a number of levels that are designed differently than in LoD, making it more than a "special edition," and you get to start with a more direct Classicvania feel due to the whip character being there from the start. If you go from CV64 to LoD, you'll see some various refinements and differing quirks, as well as new storyline insights. Also, to my recollection, you'll find that a lot of levels are easier in LoD. In effect, they may be more balanced and/or straightforward; but I sort of miss the other level designs' contrasts from CV64, even if they do perhaps have more frustrating parts. I honestly would say to play them both, and start with CV64. But that's not to say that LoD is worse by any means. They both have their pros and cons.