There is no "ideal". The best magnification is whatever mag YOU like best.
The higher the mag, the easier it is to see individual trichromes, but the harder it is to inspect lots of trichs at once.
I'd say pick the LOWEST magnification you can get away with.
30x works great, and if you like it, stick to it. I like 40-45X. Some people like to go all the way to 60 or 100x, but IMO that's too much magnification.