My models always end up slightly inclined when orbiting. This is annoying if I want to take nice screenshots, and it just slightly upsets me to see a model tilted just off of vertical. I am a big fan of the orbital controls of Dlubal RFEM: mouse only, predominantly constrained orbit, but it is possible to turn the model over and view it from below. Don't know exactly how they do it, but it works like a charm!