I am going to need to replace my Russian tort's uvb bulb soon and once again overwhelmed with the choices. I currently use the Flourescent Repti Sun, 18". I replace it every 6 months and this will be the second time replacing. Other than using the Powersun bulb, I am wondering what is the best UVB Fluorescent bulb to use between the Zilla, Zoo Med or Exo Terra brand? Any suggestions would be welcomed. Thank you!