As a data point: I met a service technician for colonoscopy equipment (in good spirits) and he said he wouldn't recommend one.
From my past experience, I'd recommend MRI over anything else (especially CT scans), though it's apparently not as useful in diagnosing bowel stuff as colonoscopies.
These are almost lateral approaches and very different from each other though, with MRI being more like a sonar scan and colonoscopies more like sending a submarine equipped with a camera into the depths.
Both can be very useful and helpful in aiding diagnosis with more data points.
Case in point, I have had an MRI (which showed nothing), several CT scans (which showed temporary blockage) and both methods have not really led to a conclusive diagnosis.
From my past experience, I'd recommend MRI over anything else (especially CT scans), though it's apparently not as useful in diagnosing bowel stuff as colonoscopies.