Bent over the exam table. It's the only way I've had it done so far.
Laying flat on the exam table with legs pulled up, exposing the anus, seems awkward and too close to...
Laying flat on your back with legs in stirrups which would be a mess. I've got a gynecology fetish...this would not end well.
In a practical medical situation, hands and knees on the exam table with rectum exposed seems a hassle to get into and frankly there's a danger of falling off the table.
blindside, you told us you've experienced them all but didn't tell us your preference.