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Fire SA
Bouncing ball PTP
Jumping SA
Water Splash SA
Door Opening Either
Frown to Grin PTP
I thought if it is unpredictable then maybe SA is better.
I think my answers where slightly different due to lack of experience. You live and you learn.
Fire - Straight Ahead
Bouncing Ball - Pose to Pose
Jumping - Pose to Pose
Water Splash - Straight Ahead
Door Opening - Straight Ahead
Frown to Grin - Pose to Pose
Agreed with the lecture on most points, but since a door always opens the same way I feel straight ahead could be simpler. But I have not tested this so I guess we’ll see 
SA = Straight Ahead
P2P = Pose to Pose
Mix is either one, of course.
But I’m not terribly confident in my answers. Let’s see what I learn when I play the rest of the video
Fire: Both
Bouncing Ball: Pose to pose
Jumping: Both
Water Splash: Both
Door Opening: Pose to pose
Frown to Grin: Pose to Pose
For the ones labeled both, pose to pose to know where the animation flow is for keys and extremes and straight ahead for breakdowns and in-betweens.
My answers to the challenge:
Fire: Straight Ahead
Bouncing Ball: Pose To Pose
Water Splash: Straight Ahead
Jumping: I think it can be done with both methods
Door Opening: Pose to pose
Frown to Grin: Straight Ahead?
Here are my answers
Fire: straight ahead
Bouncing Ball: pose to pose
Jumping: pose to pose
Water Spash: straight ahead
Door Opening:straight ahead
Frown to Grin: straight ahead
I went with straight ahead for the door because the door’s motion is restricted and it moves the same way every time. I thought this would lend itself to straight ahead since the movement is predictable.
I picked straight ahead for the frown to grin because I also thought this would be a predictable movement that would lend itself well to drawing one frame at a time.
Fire and Water Splash: straight ahead.
It’s intuitively clear, but hard to explain why… I think it’s because these movements are somewhat arbitrary and unpredictable, as opposed to a door opening, where we have a clear picture of how it looks at the beginning and at the end.
Bouncing Ball, Jumping, Door Opening, and Frown to Grin: pose to pose.
Edit: I found this challenge very good. It made things quite clear.
Straight Ahead Animation is the act of drawing out each frame from start to finish.
Pose To Pose Animation is where we determine a start and an end point, make key frames in the animation then fill out the rest of the animation to make it smooth.
In other words using “Straight Ahead” we count 1,2,3,4,5 but using “Pose to Pose” we count 1,5,3,2,4.
More visually…
Straight Ahead:
1
1,2
1,2,3
1,2,3,4
1,2,3,4,5
Pose To Pose:
1
1, , , ,5
1, ,3, ,5
1,2,3, ,5
1,2,3,4,5
Primary method for:
- Fire
Straight Ahead. Fire is unpredictable in its nature so we animate using the more organic method. - Bouncing Ball
Pose To Pose. You can use straight ahead but a bouncing ball is fairly predictable and follows a path according to mechanics. - Jumping
Pose To Pose. You tend to jump from a start to an end point. - Water Splash
Straight Ahead. Water splashes are somewhat similar to fire in so much that the splash is more organic than other types of impacts. However, you could also use Pose To Pose by taking the end state of the splash (calm water) and adding key frames for the various stages of the splash, for example, the moment of impact of the droplet, the peak of the splash, water rippling from the point of entry etc. - Door Opening
Pose To Pose. A door can only open so wide, in other words there is a start and an end point to the act of a door opening. - Frown to Grin
Pose To Pose. Despite this being quite a complex action, the very name of this task defines a clear start and end point. In fact, using Pose To Pose here can help to stop us getting off course when trying to draw the transition. The basis could be Frown - Neutral - Grin then filling in the intervals.