Soft x-ray emission spectroscopy is a well established technique which has seen increased interest in recent years due to the development of high brilliance synchronization radiation facilities. Emission spectra are obtained when a hole is created by impinging photons and an electron from the valence band decays into the core hole emitting its excess energy radiatively. The fluorescence yield is intrinsically low in the range of soft x-rays, usually less than about 0.5%, since most of the incoming photon energy is lost to radiationless decay channels like Coster Kronig and Auger processes. Emission is over all space, but only a restricted solid angle can be collected and this further reduces the efficiency of the instrumentation. Moreover, the emitted photons must be energy selected, and this involves the use of soft x-ray monochromators with good resolving power. In this work, we report the design and comparison of two different spectrometers both based on variable line space (VLS) gratings. The main constraints are the requirements of a compact instrument, good resolving power, high efficiency, and high angular acceptance. In the first case, a solution with two spherical gratings with variable groove density were utilized. The grating is fixed and the photon detector scans the energy by means of a small translation to cover all the energies from 40 to 1000 eV. In the second case the detector is fixed and a plane grating, with variable line density, moves parallel to its surface. By coupling the diffractive and focusing properties of a VLS plane grating with a single movement one can always focus the radiation at the selected energy on a fixed detector. This grating is also always in the blaze condition, thus one has very good efficiency and good resolving power in the whole range of energy of interest.