I have 2 HQ flight cages, one for my Parrotlet, and one is a sleeping cage for my GCC. I also have an A&E "Conure Castle" for my GCC's daytime cage.
The HQ cages are very well made and hold up well. The bars are heavy-duty too. The stand and the cage are two pieces, and although I really don't think the cage would slide off the stand, we zip tied them together with heavy-duty zip ties. I got my cages at Birds Comfort, here's a link to the cage I bought:
They are reasonably priced and are shipped quickly.
My A&E Conure Castle cost 3 times as much and weighs more than double the HQ -- (HQ - 50 lbs., Conure Castle - 113 lbs.), so it's difficult to compare them. I do LOVE the BIG door in the A&E cage! Makes it much easier to clean than the 2 door HQ.
Here's a link to my A&E cage:
As the site states, this cage would be great for even larger birds than my GCC, but for smaller birds, the bar spacing is too wide.
If other HQ and A&E cages are made as well as these two models, you should be fine with either brand. There is another cage, the Value Crate, which is about the same size as the HQ flight cage and about the same price, but has one bigger door, which is another good option. Here's a link to that website:
They have other models too, both larger and smaller than this cage, and they look very nice.
Here's a pic of my HQ cage and my A&E cage set ups:
Hope this helps a little!