Any Alien race that we ever come in to contact with will have built
technology either in the shape of spaceship or a radio.

If a Alien race builds machines, it is only a matter of time before the
machines are more sophisticated than the creatures that built them.  I think
it is likely that the machines will far out live their masters and go on to
build their own civilization.

The mental psyche of a machine is pure guess work, if the machines decided
to propagate themselves, they could start a colonization drive of nearby
planets.  This machine Empire would grow slowly at first, but at a geometric
rate (i.e. 2,4,8,16,32,) and in a short amount of time (only a few million
years) the machine Empire would populate the known universe.  Which,
although big, the universe is only growing at a numetric rate (1,2,3,4,5,6).

A geometric growth rate will always far out perform a numetric one.  Since
the Universe is billions of years old, at this point it should have been
fully colonized by now.  Emplty planets like mars should be extremely rare.
(I believe that the presence of empty planets are an early indication that
we are infact alone.)

I believe that it is far more likely that we will meet a machine race than a
biological one.