Alarm.com does seem to be pushing the VDB770 over the SkyBell, although the SkyBell is supported.
The biggest difference is that the SkyBell does not work with Alarm.com’s Video Analytics recording features, so its motion detection capabilities are not as robust as the VDB770. The downside is the VDB770 requires a plan with Video Analytics to function at all.
Signal strength requirements are less stringent on the VDB770 as well, allowing for a more stable connection.
More on Video Analytics here
You can see camera specs here:
SkyBell:
VDB770
https://support.suretyhome.com/t/what-cameras-can-i-use-with-alarm-com/3123/10