Never saw it as a planned implosion from the simple fact that each collapse start in the area of the aircraft impact just like you would expect...
Last year one of the networks was replaying their 9/11 broadcast in real time. It was pointed out to me that the second plane struck the second tower at a much lower level than the first, in order to increase the effect of gravity on the structure-weakening fire.
And it was the tower that was struck second which was the first to collapse.
Controlled implosions start from the bottom up for exactly the same reason, IMO.