You need to work out what your valuation is now and what it is predicted to be when you take your next round of investment. If you take the 10M for 20% and then

You need to work out what your valuation is now and what it is predicted to be when you take your next round of investment. If you take the 10M for 20% and then sell the next 20% for less than 10M you are telling your investors that the investment has devalued. You would think that you want to claw as much money from their hands but that comes back on you if you don't think you can grow or maintain the value your company is currently at.