Hm, I tried to respond for myself and formulate it properly, but I think it will be better to just post some old creeds and to say I agree with them so that I will not be inventing a wheel again:
The Nicene Creed (385):
We believe in one God, the Father Almighty, Maker of heaven and earth, and of all things visible and invisible.
And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds (æons), Light of Light, very God of very God, begotten, not made, being of one substance with the Father, by whom all things were made;
And for example The Second Helvetic Confession (1534):
"GOD IS THREE. Notwithstanding we believe and teach that the same immense, one and indivisible God is in person inseparably and without confusion distinguished as Father, Son and Holy Spirit so, as the Father has begotten the Son from eternity, the Son is begotten by an ineffable generation, and the holy Spirit truly proceeds from them both, and the same from eternity and is to be worshipped with both.
Thus there are not three gods, but three persons, cosubstantial, coeternal, and coequal; distinct with respect to hypostases, and with respect to order, the one preceding the other yet without any inequality. For according to the nature or essence they are so joined together that they are one God, and the divine nature is common to the Father, Son and Holy Spirit."