If in a Delta Lake table you only store (lat, lon) values, use GEOGRAPHY (with the caveat that for st_distanceshpere and st_distancespheroid to work, you would need to cast geographies to geometry as geog::geometry(4326)).
If you use an SRID other than 4326 or multiple SRID’s, use GEOMETRY. If you need to calculate values in meters from lat/lon, you can still cast to GEOGRAPHY as needed and use measurement functions like st_area, st_length or st_perimeter.
If you need compatility with other tools, you might consider WKB – however, spark.write.parquet() would export GEOMETRY/GEOGRAPHY columns as WKB anyway.