GS90C. It runs the Ambarella A7 chipset which is great quality. I have that as my front facing dashcam and a G90 (older internal hardware but same external look) as a rear facing camera.
The GS90C has a GPS addon that displays your speed in MPH beside the timestamp. That camera also allows for 1920x1080 60FPS footage to be recorded. I like the higher framerate because it allows for smoother looking video and easier for it to capture finer details such as license plates when moving at higher speeds. If you don't feel you need that, the G90 will work for you and costs less.
Here's the GS90C: GS90C Ambarella A7LA70 Full HD 1296P Car Dash Camera DVR 170° 2.7� G-sensor [GS90C]FoxOffer - Wholesale, OEM, Drop shipping from China directly
Here's the G90: G90 1080P Full HD Ambarella A7LA30 Car Camera DVR [G90]FoxOffer - Wholesale, OEM, Drop shipping from China directly
If you haven't heard of FoxOffer, they're a great site. They're based in Hong Kong or China or something so if you send support emails their replies are rather vague but I've ordered both my dash cams from them and the shipping is free, takes a while to arrive, but has been very reliable.
Here's a dashcam compilation I threw together. https://www.youtube.com/watch?v=jkKM_RjFPgs All footage is from my G90 Dashcam. I can put up a demo video with 2 clips from my GS90C camera shortly for comparison.
EDIT: Here's a brief demo video of the GS90C footage recorded at 60FPS. https://www.youtube.com/watch?v=nKBWJ-jxvPo