The emergence of several ontology modeling tools is motivated by the growing attention ontologies receive in scientific and industrial contexts. The available tools implement different ontology modeling paradigms, including text-based editors, graphical user interfaces with hierarchical trees and form widgets, and visual modeling approaches based on node-link diagrams. In this paper, we present an empirical user study comparing a visual ontology modeling approach, based on node-link diagrams, with a modeling paradigm that uses hierarchical trees and form widgets. In particular, the user study compares the two ontology modeling tools: Protégé and WebVOWL Editor, each implementing one modeling paradigm. The involved participants were given the tasks of ontology modeling and also answered reflective questions for the individual tools. We recorded completion times of the modeling tasks, the errors made, and users' understanding of the conceptual spaces. The study indicates that visual ontology modeling, based on node-link diagrams, is comparatively easy to learn and is recommended especially for users with little experience with ontology modeling and its formalizations. For more experienced users, no clear performance differences are found between the two modeling paradigms; both seem to have their pros and cons depending on the type of ontology and modeling context.