We present the results of an evaluation of effective text representation suited for virtual reality scientific data analysis applications. The increasing popularity of VR displays in scientific research requires a transfer of visualization and text representation techniques from traditional desktop systems into immersive environments. However, particularly in text rendering not every aspect of 2D displays can be replicated in immersive systems. To analyze which aspects are most beneficial to text legibility, we conducted a user study to evaluate the effects of text panel placement and rendering methods on reading speeds in generic volumetric particle visualizations. By measuring reading performance in three state-of-the-art VR displays (two head-mounted displays and a CAVE) we collected insights that are generalizable to a large range of VR systems. Our results show significantly improved reading performance when occlusions in front of tooltips are removed and some minor benefits of orienting tooltips towards the user. We also found significant benefits of higher display-fidelity on reading speed and visual acuity, leading to guidelines of effective tooltip text representation.