I personally tend to prefer places as nodes, but there isn't a hard-and-fast rule. Sometimes when the building is exclusively used by a single business it makes sense to tag the shape, but in most cases it makes the most sense as a node.

The web editor has a feature where you can right-click on the shape and use "Extract" to pull the place information out onto a separate node.

Also, check out the app "EveryDoor" or "StreetComplete" to make mobile mapping easier.