What are some factors to consider when choosing (or creating) the right sound
effect for a door opening?

I would say to mostly look at the pitch of audio clip, depending on your intentions, along with considering the context of the environment when this noise will occur.

For instance, perhaps you want the door to open "normal sounding", then you would seek to pick a lower pitched noise that doesn't grab the audience's attention as much. By doing this, it would sound more seamless with the rest of the video, play, presentation, or whatever you're doing.

However, if you want a loud screechy door, look for one with a high pitched noise and one that's attention seeking. Therefore, it graphs the audience's attention by making them pay attention to what is going on. However, use this to highlight that an important action is about to occur, rather than just a random part of the production, as you probably don't want to annoy your audience.

Hope that helps.