Data centers have an extensive range of complicated system design choices that can often seem overwhelming when deciding on the best way to optimize system design for reliability and energy efficiency. Is an air-side or water-side economizer system better, or should an indirect system be used over a wet-bulb economizer design? Is the industry moving away from raised floor designs to installing server cabinets directly on slab? High-level decisions can be complicated and diving further into the details can reveal even more trade-offs and choices. Should containment be done on the cold-aisle or hot-aisle? Is it better to select units with electronically commutated (EC) fans or VFD-equipped motors? The authors present a range of topics for debate in data center design, discuss the strengths and weaknesses of each, and review their applicability and limiting factors. These highly contested topics are being debated among designers and operators, end users and owners. Readers are encouraged to participate in these discussions to contribute to the variety of viewpoints on complex data center systems design.