Example: assume the valuations each year are 0.10, 0.20, 0.30, 0.40, 0.50 and the sale price is $1 at year 5.
In option 1 your strike price will be $0.10 for all 100 options so should you choose to exercise you have to pay $10, netting you $90. You can choose to exercise these as they vest, paying $2.50 each year. If you choose to exercise on vest, your cost is the same, although you potentially will owe AMT.
This means that if you make enough money you essentially have to declare the difference between strike price and current value as income. This means you will have to potentially pay taxes on an extra $25 over the four years.
In option 2, exercising the options will require $5.00, $7.50, $10, $12.50 for a total of $35. This means you only make $65 in the sale.