A vote for stroke thought
I picked up TI less than a year ago when I bought the Easy Freestyle DVD, so I've heard the term "Stroke Thought" more than focal point, so that may have biased me a bit in favor of Stroke Thought. But here's my reasons for the preference:
1. Ties to whole stroke swimming, even when beginning to learn to swim via TI lessons from scratch. The term suggests that what I'm doing when learning a drill is a "thought" I can have when swimming the whole stroke later.
2. Reminds me that when swimming whole stroke, at any speed, I should have a stroke thought for each stroke, whether for the whole practice, one length, or just the stroke I'm taking at the moment. Since it's a stroke thought, I can change the thought after a stroke or two, or hold it for more strokes.
3. The word "thought" emphasizes using your mind while swimming to improve.
4. Stroke thought seems to be a relatively unique term, if not unique to TI then at least to swimming (though perhaps also golf). Focal point seems more generic and could apply to any sport or other activity.