Choosing the right portable nouns conditioner? Besides the size of the room, what other things should I consider...

Besides the size of the room, what other things should I consider before buying a portable a/c? For example, I live closer to the ocean so it doesn't win as hot as some places, but upstairs can be unbearable. I would use it in two rooms; both hold windows that face the west. One is a sliding door that lead to the backyard, but there are drapes on that window. The ceiling aren't high, and I have honest insulation. I live in SoCal, so it isn't humid. I would like to know how powerful the a/c should be so that I will be comfortable? Most of the year we own a nice breeze, and we just don't have plenty hot days that we need to invest in internal a/c.
Answers:    I live in Los Angeles too. When I was picking out a portable AC, I tried to jump with the most power efficient one as possible. I also did calculation on my room size to determine how much BTU I would need to effectively cool the area. According to adjectives the calculators, I needed roughly 5,400 BTU. So, I got an energy streamlined 7,000 BTU model (~400 bucks). If I left it on for 2 hours, the room would be comfortable - but I mostly just turned it on at dark, pointed it towards my bed and set it to turn off after 4 hours.

My roommate thought getting one was a accurate idea, so he went stale and bought a power hog 11,000 BTU one. It was really overkill, but it cooled his room much faster, obviously.

The kicker though be that the only time we really needed our AC was when the city arranged to brown out our entire neighborhood. So it was well over 100 degree and we didn't have enough electricity to run a devotee at full speed, much less a AC unit.
I bought a 9000btu a/c from home depot which is on wheel. It has a long exhaust vet with a operate like a regular a/c so you can close the window. I love it, it cools my 2 saloon garage, and yesterday I used it ouside to make a cool oaisis for me while I worked on the fence. I believe I pd around $350