Define "best". We've used a quarter million dollar one at my current company, and at a previous job we spent far, far more than that for military airframes. Gr

Define "best". We've used a quarter million dollar one at my current company, and at a previous job we spent far, far more than that for military airframes. Groves "Principles of GNSS, Inertial, and Multisensor Navigation Systems" contains a good description of the various technologies used and their accuracy limits for navigation. Consumer grade MEMS are fine for airbags, the pedometer in your phone, but are not sufficient for intertial navigation, even when aided with other sources. At around the $2K-30K you get systems that can provide accurate navigation for up to 2 minutes or so. They are used in things like missiles. Aviation grade IMUs need to meet SNU 84 standard, which requires a maximum horizontal position drift of 1.5km in the first hour of operation. These will run 100K and up. Marine grade (subs, rockets, ICBMs) run $1 million and up, and have a maximum drift of 1.8km per day. None of them are good enough for autonomous cars w/o sensor fusion.