[ilyanep]

I am not an accountant, this is not tax advice.

You're usually correct, except for two things (in the US):

1) Holding stock for a year before selling is taxed at the lower long-term capital gains rate (~20% vs ~39.6% at the highest brackets).

2) Exercising an ISO is seen as a taxable income for the purposes of the Alternative Minimum Tax, so exercising late (when the difference between FMV and Strike Price is high) has a higher chance of incurring an AMT burden, whereas exercising early does not incur an AMT burden (because the spread is small) nor a normal tax burden (because this is how ISOs work).