Blake Griffin is having a tremendous January and February. His offensive game is much improved. He's still lacking some defensive prowess though. Right now he is just bullying LaMarcus Aldridge. Given that we know Dwight Howard is pretty much at his peak and his offensive game won't be truly dominant (although sometimes effective), would you rather have Blake Griffin on this team or Howard?
Howard. He's very valuable as a rim protector and it's much easier to find the perfect 4 to complement Howard than it is to find the perfect 5 to complement Griffin.
Howard because of his defense, it is a lot easier to replace Griffin's offense than Dwight's defense imo.
Blake is damn awesome and will become even better, but for Houston, Dwight is more suitable and just as good of a player at this moment in time.
For the Rockets in particular its Howard because the Rockets defense blows. However, now that I think about it the Rockets could have Blake Griffin at the PF spot and Asik as the starting center. So I guess I go with Blake. He has been a force of nature as of late and keeps getting better.