Should I read S;G and S;G 0 in Japanese or English? Which is the better experience? I presume you played both versions.

Ultimately it comes down to preference. They're both very different experiences, as in the translation process the translator adds his or her own flair to the text. Also certain terms are handled differently. If you want more things you're familiar with, I'd say the English version, but if you're just wanting to read the VN as it was originally presented, go for Japanese.