Not having ADS-B in my part of the world, nor likely to for many years, I can't add anything much to the conversation, except to say that in my aircraft I have an SV puck on each of two displays and both a GTN750 and GTN650, each with external GPS aerials.
(The aircraft flies over a lot of water and TSO'd navigators are required by our regulations, even for VFR, when more than 100 nm from land)
I can tell you that the SV pucks are at least as accurate as the Garmins, however, any differences in position update and "jumpiness" are not noticeable with any of these sources at an average groundspeed 0f 135 knots.
Were I not required to have TSO navigators, I would be more than happy to be in the middle of the Pacific with a GPS 250 as my main nav source.