The Rainbow is an excellent unit. Very powerful airflow and great agitation. The side spinning brushes are like a street sweeper along a curb, it really does pull hair and junk in from baseboards and furniture. Several great things about the Rainbow also include: blower function, wet pickup ability. I have found that the current model is one of their most powerful suction units yet.
The Filter Queen is a good vacuum. I used to sell Filter Queen and Rainbow and in doing a comparison I felt the Rainbow was finding more sand and grit while the Filter Queen was down to just collecting carpet fiber. The test was very surprising to me because the new Filter Queen does have very soft bristles on the agitator. It is important to note that the Filter Queen with a new cone and filters in clean shape, the airflow is quite impressive!! While the power nozzle is good, it's not as good as many other power heads on the market. I never noticed any issue with the elbows on the units. They are plastic and rotate, but I never noticed it as being a weak spot of the machine, it just sounds like a crappy loud snap when you unlock the wand into operating position.
I have tried the TriStar MG-1 and MG-2 series. They are very durable, whisper quiet, and a neat looking design with great filtration. However I thought the airflow was limiting. Quite undpowered compared to the Filter Queen, Rainbow, Kenmore and many other machines on the market. Agitation was ok, could be stronger and more airflow would help that factor too! The cord wrap on this is horrific, you may as well just wrap it up in your arms and throw it over the hose or something!
Not sure if you've considered but Simplicity/ Riccar machines are QUITE powerful!! Excellent agitation and very powerful airflow. They have several models available including the new Prima/ Wonder series that has impressed many thus far.
Older style Tri-Star CXL type series I've heard to be very excellent, high powered machines. I haven't yet tried one myself but I have yet to hear a negative about them.
Also while some of the high end Aerus machines have a neck issue, I don't believe that holds true with their entry level classic style power nozzle. You may lose the headlight, and newest filter queen lacks that too along with all of the Tri Star machines lack a headlight as well.
Best of luck in your search!