Physical activity (PA) provides great health benefits for people with spinal cord injury (SCI). Consequently, the design and implementation of PA interventions addressed to this population is needed. To rigorously evaluate these interventions, the use of valid and comprehensive PA measures is crucial. Since the suitability of PA assessment tools might differ among different populations, and considering that questionnaires are one of the most frequently used tools to quantify PA, the purpose of this comparative review was to examine nine questionnaires that have been used to assess PA in people with SCI. All the questionnaires were analyzed in depth in regard to three main dimensions: (1) SCI-specific development; (2) PA domains measured and PA intensity classification; and (3) reliability and validity. After careful consideration of the evidence available on all these aspects, it is suggested that the most suitable questionnaires to be used in PA research in the SCI population are the PARA-SCI and the LTPAQ-SCI[R]. To conclude, the strengths and limitations of these two questionnaires are discussed, and specific recommendations to SCI researchers and practitioners regarding the suitability, according to the context and characteristics, of the research/intervention are provided.