The foam will have R-values from R4 + per inch the Celotex will have R-value of 1 per inch (of thickness). The Celotex will provide better sound insulation, the foam will retain more heat in the grow area. My choice would be just a covering that is white unless sound insulation is a necessity, then the celotex. Even Sheetrock will help with sound, structural integretity and have a good solid surface for any future modifications.

Regardless all walls white!