Unfortunately cage buying is something I've done pretty rubbish at because there isn't really anywhere that sells a good selection of them round here so you can see them. I usually have to order online. I find it near impossible even with pictures and measurements to visualise what they would be like practically.
All the cages I have ever had have had faults, I had one come with a guillotine style door which can be downright dangerous. The door design wasn't apparent in the picture/description but to be honest the cage was otherwise perfect, including for ease of cleaning so I put clips on the doors to prevent them being lifted by the bird and to hold the door open at out times. I was always very very careful when opening or shutting it that the bird was far away from it in case I accidently dropped it.
Most of the cages I've had the doors have been impractical on though- they were usually on the small side for the size of cage, It's really something I should have learned to take into account by now but I still ended up buying another cage a couple of months ago where the door is too small

This worries me in case I ever have an emergency and need to get the birds out quickly. With Ollies cage it is also impractical as I have to remove the bottom tray and physically crawl underneath and inside to fit new toys. Luckily I'm only 5'2" so I can stand up inside ok and I'm still young enough to get down on my hands and knees and crawl underneath without too many problems lol.
Another big issue I had with one cage I owned is the bars were not completely welded together. I got it seeing a nice big cage which looked easy to clean, had a nice big door, high feeders, not long after I hated the darn cage. Food got stuck in between the bars, water collected in the gaps and caused the end of the bars to rust which soon spread upwards and started to cause the powder coat to loosen..... never again...
I guess safety and ease of cleaning are the most important issues for me, although if I were able to design a cage I know exactly how it would be