Don't really dread any single pin leave but if I had to pick any it would be 4-pins and 7-pins. I'm a righty, very very seldomly miss single pins, but the 4 & 7-pin leaves often causes the odd difficulty on some of the very patchy backends we get here at times.
I had to change when the synthetics were installed here from shooting those spares straight down the 4th arrow (on the old wooden surface) to shooting them off the 2nd arrow because I'd be constantly sliding by them on the newer surface - worked that out in the first 2 games I ever bowled on the plastics.