renaissance poisson

From the perspective of knowing something about Polynesian languages, I prefer a macron, although using one over a consonant just seems WRONG (although obviously appropriate for Japanese). If it is used consistently to indicate a long vowel instead of a short one, it's reliable, IMO.

Macrons rather than doubled-vowels clearly indicate when there is a single sound rather than two (important when there is the kind of glottal stop you get in Samoan, etc). Using a diphthong when it's a single vowel seems potentially inaccurate (since I believe the "o" in Tokyo is supposed to be an /ɔ/ rather than /oʊ/), as does the "oh" rendering.

The circumflexes seem slightly odd to me from having studied French, but if used consistently, they seem to be like macrons in their usefulness (slightly edged out IMO by macrons, since the latter are not used in a quite different way in another language). Difficult problem, though!