A good softbox for a small hotshoe flash depends on your priorities: portability, durability, size, and cost. In general, a larger light source gives softer light, but larger modifiers are less compact.

From the community suggestions, the Lastolite Ezybox is a strong option for speedlights, with one user specifically recommending the 60x60cm version as versatile and even compact when packed. The LumiQuest Softbox III was also mentioned as a speedlight-friendly option, though more as a smaller, simpler modifier.

Another approach is using a hotshoe bracket/adapter so your flash can mount to a standard softbox. If portability and simplicity matter most, you might also consider a shoot-through umbrella instead of a softbox, since umbrellas are often easier and faster to set up.

So the practical answer is:

• For a dedicated speedlight softbox: Lastolite Ezybox is a well-regarded choice.
• For compact/simple use: LumiQuest Softbox III.
• For easiest setup and value: shoot-through umbrella.
• For more flexibility: a hotshoe adapter with a regular softbox.