For the first look after surgery, I would go with the surgeon. For all other colonoscopies, definitely the gastroenterologist. That's what I did.
Nov-2009 Early stage CRC found during routine colonoscopy
2010, 2011, 2014 Follow up colonoscopies, all clear
Jun-2016 CRC found during routine follow up colonoscopy, surgery, Stage 4, KRAS, inoperable lung mets
Aug-2016-May-2018 Folfox, 5FU & Avastin, 5FU, Folfiri & Cyramza
Aug/Sep-2018 YAG laser surgeries (Germany) on both lungs, 11 nodules (9 mets) removed
Oct-2018 ... holding pattern
Mar-2019 New nodules reported