[jpab]

For viewing objects I find a turntable style view best in most circumstances. For landscape or architecture (where you're in the scene), mouselook with WASD + vertical up/down.

Neither of these control styles are 6dof; they don't provide a roll control, only elevation, azimuth and position. Roll is rarely useful IMHO and including it in the normal control scheme makes things hard to use. Put roll behind an explicit modifier key, and have a reset-roll action somewhere.