It depends on what method you choose to knit.
Single needle set in the round - 16" plus either another one for the top or DPNs in the same needle size.
Magic loop - at least 24" for modified ML or 32"+ for standard ML. Suzeeq likes shorter ones, some people prefer longer.. it's personal preference.
29" would work for various things though maybe not all. That's why many of us use an interchangeable set.