I assume you are paying normal income tax on the shares when they vest. At that point, they are just shares that have a cost basis for the Fair Market Value on the day they vest. If you sell them immediately, there will be essentially no additional taxes. This is what I do. I have no desire to hold individual stocks, especially in my company. I want to maintain a well diversified portfolio. I already have my job and NQDCP in my company. That is enough.
If the stock is a small enough percentage of your portfolio and you are comfortable keeping the stock, then keep them. Otherwise, sell them.
In the future, I would recommend selling any new shares as soon as they vest.
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