In biology, “primitive” and “advanced” are relativeterms, and are typically (though by no means exclusively) used when describing traits of an organism rather than the organism itself.
Evolution is a goal-directed process, but not in the way the question suggests. People often get the false impression that evolution is a ladder, each of the rungs representing a higher, more advanced creature, and stopping at our species as either the perfection of evolutionary advancement, or as the most advanced creature achieved so far. This is a notion that demands evolution be constantly striving toward the bigger, better, more "advanced" creature.
I will say facultative, because I think this type of bacteria has a more flexible biological system that qualifies them to deal with various habits.
I would say that it depends on what sort of condition the microbe is obligated to live in. For example, being an obligate anaerobe is likely a very old development on the evolutionary timeline, with facultative anaerobes developing during the great oxygenation event, and then obligate aerobes developing as the anaerobic metabolism became less vital in certain environments.
Facultative adaptation to a condition could be seen as an "intermediate" step in the evolution of microbial populations from one condition to another. I think whether facultative adaptation or obligate adaptation is more advanced largely depends on the context of what condition is being looked at. I don't think one is inherently more advanced, as a move towards obligated-ness away from facultative-ness could be loss of unnecessary traits for improved genetic economy, or shutting down of their expression to maximize metabolic efficiency.
That being said, everything I said is complete speculation/opinion.
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