Yeah, the katakana for 'ko' is there and I'm a bit like, 'hmmm...' but the sheer amount of people that know it as Neco and Necoco kind of persuades me. I could leave it, and if anyone has issues with it then could deal with it later. The site I read the manga on calls it Neco, which is why I originally grew attached to the name: http://mangafox.me/manga/love_neco/

Who knows. I think, as you said, it's probably down to preference, and I see 'Love Neco' a lot more than the other spelling. Like you also said, it does look better (and more original) with 'c's.