Great White or Basking

[Fish On]

Saw a ashark yesterday while trolling. First spotted the fin and decided to troll near it to get a better look, expected to see a sun fish. Shark was about 16 to 20 feet in length. The dorsal fin was somewhat rounded at the top. I could also see the white underside from the pectoral fins forward, but beyond that I coulnd't make out any distinguishing charateristics. Any experts have an opinion? Water was about 66 degrees F, 250 feet deep.