Of the 6 I see number 3 as the most likely. Advanced civilizations are probably rare, and we are probably the only one in our bubble of influence at this point in time.
That depends on how you define 'advanced'. Compared to what else is most likely out there, what we had ten thousand years ago is 'advanced', even technological in its own way.
Still, I agree, sentient culture probably is rare. Otherwise I think even with our relatively primitive technology and half-assed efforts so far, we would have heard something demonstrably of ETI origin.
Anyway, we already know item #1 is false, at least as far as automated probes go, since one of the Voyagers is now outside the heliopause and in interstellar space.
Item #2 is statistical only. Due to the time and space constraints it's likely, but it's not necessary.
Item #3 is highly likely due to time and space constraints. If (as I think likely) there are only a small number of sentient cultures in the galaxy at any particular time (I peg it at 4-6), the average distance between any two is thousands of light years and the time difference between any two having comparable levels of development is profoundly variable.
Item #4 pre-supposes that there is an über-sentience out there waiting to knock down all possible rivals. Not impossible, but not bloody likely, I don't think. A galaxy-wide sentient civilization cannot exist without leaving some
detectable trace of itself, so #4 is probably unlikely enough to be discounted.
Item #5 is tautological if technological civilizations are rare in the first place.
Item #6 is entirely possible. Assuming the principle of mediocrity forces us to assume we are not alone in the universe at a minimum, but there's no reason we can't be the first or the only. I think 'the only' flies in the face of statistics, but that's not demonstrated.