While sitting is a common aggravating factor in low back pain (LBP), the best sitting posture remains unclear. This study investigated the perceptions of 295 physiotherapists in four different European countries on sitting posture. Physiotherapists selected their perceived best sitting posture from a sample of nine options that ranged from slumped to upright sitting, as well as completing the back beliefs questionnaire (BBQ). 85% of physiotherapists selected one of two postures as best, with one posture being selected significantly more frequently than the remainder (p < 0.05). Interestingly, these two most frequently selected postures were very different from each other. Those who selected the more upright sitting posture had more negative LBP beliefs on the BBQ (p < 0.05). The choice of best sitting posture also varied between countries (p < 0.05). Overall, disagreement remains on what constitutes a neutral spine posture, and what is the best sitting posture. Qualitative comments indicated that sitting postures which matched the natural shape of the spine, and appeared comfortable and/or relaxed without excessive muscle tone were often deemed advantageous. Further research on the perceptions of people with LBP on sitting posture are indicated.