Worst: TAR 10 in Finland. Mud, cave, rappel. They could've gone pretty much ANYWHERE in the continent (or world) for those sets of tasks.
Best: TAR 3 in Grindelwald. Testing teams' travel skills, mental acuity, physical dexterity and endurance all in one leg? I love it.
Honorable mentions: TAR 17 in St. Petersburg (first Detour was great, second RB and miscellaneous tasks were great - they could've had the BEST LEG EVER with a bit of reconfiguration but they settled for two good legs), TAR 12 in Italy (difficult tasks + self navigation + several forms of transportation to cause people to get loopy and hateful toward each other? good times)