Recently, we demonstrated the feasibility of a novel 3D silicon bulk-micromachined accelerometer with an optical or a capacitive read-out. In this paper we will compare both detection techniques, and also show their potentials and limitations. The mechanical elements of the accelerometers are fabricated by an unconventional wet etching process of (100) silicon, resulting in symmetrically suspended seismic masses with a high lateral sensitivity and very low transverse sensitivities. For the detection of the seismic mass displacement under the effect of an acceleration, two possibilities are investigated. Firstly, by forming a Fabry- Perot cavity between the seismic mass and the output of an optical fiber, the acceleration can be sensed by measuring the optical path change. Secondly, comb shaped electrodes have been implemented to form a capacitive transducer. Both techniques can be used to build a 3D accelerometer system. Finally, we show that the noise floors of both devices are on the same order of magnitude, leading to a potentially high sensitivity (down to 1 (mu) g/(root)Hz). The optical device shows the advantage of multiplexing capability, passive fiber alignment, distant read-out, and immunity to electromagnetic interference. The capacitive transducer has beside the general advantages of an electrostatic transducer (such as possible closed loop-operation, wide temperature range, low power operation) a linear capacitive change versus displacements.