74HCT14 schmitt trigger doesn't improve rise/fall times
It looks like you've got the oscilloscope displaying some uber-expanded portion of a capture- it's only changing slope every two horizontal divisions .. so anything faster than that all looks the same. 

The first photo shows it changing slope every division, rather than two divisions in the bottom two photos, but in each case it's 20\$\mu s\$ per division, which implies your effective sample rate is only 50ksps, as @RJR comments. 

If you want to see 74HC rise and fall times, 1Gsps would be more appropriate.