Green pass or standard?

Hi! My name is Rebecca and I will be travelling across Japan from late June to the end of August (65 nights!). I will definitely be purchasing three lots of 21 day train passes, however my dilemma is whether or not to get the green passes or standard ones.

I realise it is recommended to get green passes as I’m going during festival season and it’ll be a SUPER busy, but I’m really struggling to find a website or anything that clearly explains the advantages/disadvantages of green and standard passes.

Is there anyone that could recommend whether to get three greens or three standards?

For an idea of what I’m doing, I plan on visiting places in this order:

Fly to Tokyo (stay for a night, then a week in each place)
Hiroshima
Fukuoka
Kyoto
Osaka
Morioka
Fukushima
Tokyo (and then travel to Hokkaido or other places from Tokyo, as there are trains from Tokyo to EVERYWHERE I swear)

Please help me!