Well, that question is just confusing because everyone knows that best ROM is the stock ROM, but if you are an technology geek and want to try something new on your device you can go forward with the custom ROM i.e you can try using the ROMs like cyanogenmod, Supersonic, slimbean etc. I'll say why don't you try googling out I am sure that you are going to find a collection of ROM available for your moto g.