mongodb geoNear vs near
Efficiency should be identical for either.
geoNear's major limitation is that as a command it can return a result set up to the maximum document size as all of the matched documents are returned in a single result document. It also requires that a distance field be added to each result document which may or may not be an issue depending on your usage.
$near is a query operator so the results can be larger than a single document (they are still returned in a single response but not a single document). You can also set the maximum number of documents via the query's limit().
I tend to recommend that users stick with the $near unless they need the diagnostics (e.g., distance, or location matched) from the geonear command.
These are major differences :-
$geoNear also gives you distance from the point but $near command doesn't.
$geoNear command requires that the collection have at most only one 2d index and/or only one 2dsphere index whereas geospatial query operators like $near and $geoWithin permit collections to have multiple geospatial indexes.This is because in $geoNear command there is no option to specify the field on which you want to search, where as in $near command you can specify the field name.
The main difference is that $near is a query operator, but $geoNear is an aggregation stage. Both return documents in order of nearest to farthest from the given point.
What it means is that $near can be used in find() queries or in the $match aggregation stage, but $geoNear cannot. Instead $geoNear must be used as a separate aggregation stage only.
The options each feature provides also differ. I invite you to review the details in the corresponding documentation sections: