Viruses need host cells to reproduce. They have no ability to reproduce without hijacking a cell, turning it's mechanisms of reproduction over to the virus, which uses them to reproduce. Since it cannot reproduce without a functioning host cell it isn't possible for a virus to be the first creature; as it would have immediately gone extinct.
Nah... it just waited. Viruses are not exactly alive to begin with, so it's difficult for them to die. There was no need to reproduce until there was something to feed on.
In actuality, no one really knows which was first, as we haven't even resolved the chicken or the egg scenario to begin with.
What cell, or creature, do you think was first ?