I will use Pentel, but prefer 0.7mm, as 0.5 is still quite easy to "break", but 0.9 mm is thick, the word is not nice. This is my comment, hope it will be useful to you.
just a further of mine. But I might be wrong.
HB is the medium quality, H - may means "hard", b - I forget, may be soft. The no before b/h is degree of hard and soft. so, you better try which one is much suitable for you. As different people may have different "pressure" in writing. When I was small, I have use those different degree of pencil in drawing. Hope it can be of some use.