Devices - there is atleast one spot on every map where devices can ruin the game. Giant is probably the only exception I can think of. Jade, in particular is notorious for this.
There is one spot near and facing the main opening from the LZ which can be an absolute nightmare if the enemies are spawning opposite the LZ while Ravagers down the ramp have LoS on you. It very rarely occurs, but it has caused me to wipe on one occasion as I ran out of time trying to kite them away.
The Jade one is really bad with the wrong team. The crate of doom on Hydra is really bad even with the right team. I tend not to mind Goddess so much, but maybe that's just because I'm more concerned with how few frames I have to work with.
The centre of Condor can be pretty tough, but I usually really enjoy it. Unlike the centre of Rio, which I don't.
In general though, the toughest device placement is the one on the opposite side of the map from the pug who's using missiles.