For freezing motion, the key spec is flash duration, not just brand name or watt-seconds. In studio high-speed work, the flash pulse often freezes the action, so you want lights with very short flash durations.

From the answers, Paul C. Buff Einstein units are a strong monolight option because they use tail-trimming, which gives shorter flash duration at lower power—good for stopping motion. They also have a color-consistent mode, though that mode is less optimized for maximum action-freezing.

A pack-and-head system can be even better in some cases. Certain Elinchrom/Profoto-style pack systems with specialized heads can produce extremely short flash durations, especially when matched to the lowest-output pack that still gives enough light.

Important pointers:

• Compare specific models, not just brands.
• Look up flash duration figures (t.1 is more useful than t.5 for real motion freezing).
• Many strobes get shorter flash duration at lower power.
• Speedlights can also have very short durations, though with less power.

So: if you want monolights, Einstein-type units are a good fit; if absolute shortest duration matters most, consider a suitable pack-and-head system.