Excellent question.

Sega-The Lost World - quite involved to shop the machine, have to remove almost everything at the back of the machine.
Batman Forever - same as above. All the stuff up the back left makes removing lots of stuff neccessary.
BK2000 - easy to shop
Godzilla - easy to shop
Next Gen - easy to shop (when your secret weapon is Beaky) lol

As for very difficult playfield shots, Last Action Hero has a shot where the ball gets shot back at you very fast, if u can get it.
Teenage Mutant Ninja Turtles has a few hard shots incl "Save April".  Ninja Ninja ! What a fun machine.

The hardest shot on any pinball, is when your wife comes in, to ramble about her day, and starts to ask questions, right when you are having a magic ball, and u are scoring really well, only to instantly get a drain ball. Its then like "GO AWAY WIFE". LOL