Final answer:
A quad cane is most suitable for a client with poor balance, offering a wider base of support and improved stability compared to canes with a single end or axillary crutches.
Step-by-step explanation:
The most appropriate type of mobility aid for a client who has poor balance is a cane with four prongs on the end (quad cane). This design provides a broader base of support and greater stability due to the larger area in contact with the ground. It is beneficial in supporting individuals who struggle with balance issues because the four prongs enhance the stability more than a single-ended cane, whether it has a half-circle or straight handle. Axillary crutches are typically used for those who need to keep weight off one leg completely, not just for poor balance, and may not be the best option in this scenario.