Hi,
I'm not one of the experienced ones but I'll give you my thoughts anyhow.
Firstly, I think that either technique works acceptably well in your C172/PA28 class of aircraft that a lot of PPL's fly. It's mostly when you get into bigger, heavier aircraft (even light twins) with more inertia that using the correct techniques matter.
You're also correct in saying that either technique <i>could</i> be used, but there is an easiest one to use at different times.
Generally, final approach is most easily flown controlling speed with power, glidepath with attitude and alignment with bank. This works better on heavier aircraft as their greater inertia means that power changes will take much longer to affect the glidepath, whilst pitch changes will be much for effective. Obviously if you change the attitude you may need to change the power setting, but as you say it's a circular argument.
The exception to the technique above is during descent on a base leg or on an ILS. For these situations the easiest technique is to set the power as required for the rate of descent and adjust the attitude until you get the speed that you desire. Then adjust the power as req'd for the RoD and attitude controls speed. (e.g. Base in a C172 is flown at approx. 1500rpm, setting the attitude as req'd to acheive the required speed and flightpath).
I've found that those techniques seem to work best, as a lot of people I've seen who have been taught to fly a light plane with the opposite techniques have a lot of difficulty adapting when learning to fly a bigger aircraft or flying ILS's. They either (a) have dreadful speed control during final approach or (b) keep poling the attitude back and forth to maintain an ILS glidepath.
So yes, there are different situations where different techniques work best, and they don't necessarily have to be at the ends of the flight envelope.
Just my opinions anyhow, be glad to hear some others.
Cheers,
Grade 3