What is bigger: a globular cluster or a nebula?
By nebulae, if you mean the planetary nebulae or supernova nebulae, then Globular clusters are bigger than nebulae.
Both planetary nebulae and the supernova nebulae are the debris left by dead stars. Whereas a globular cluster is a spherical dense cluster of stars that may have few ten-thousands to few hundred-thousand stars. They themselves may have nebulae inside them.