Long term incentives - stock options

I receive yearly stock options with my company (AstraZeneca) at 7% my base salary. They are fully vested after 3 years and at the 3yr vested mark the company subtracts some shares to over the taxes and I am left with the rest of shares to do what want (sell or hold). Example, awarded 100 shares, after 3 years company uses 30 shares to pay taxes = 70 shares for me at awarded price (i can sell or hold)).

I have generated 28K so far but I was wondering if it would make sense to sell them (especially the older ones which if i do sell would be long term gains for income tax) and invest in my brokerage as TDIF?

Option prices range from $30 - $50 depending when I got them. Just trying to learn how to make the most with this money (keep as options or roll over into brokerage as TDIF?) Welcome all advice.