Fish or Coral first?
I do a fish then a clean up crew shortly after if all is well. My reasoning for this is the clean up crew needs something to eat or they're pointless. They could run out of food fast if I'm not adding nutrients to the tank. Plus, I want something swimming around to look at. I suppose I'd be entertained enough if I had a large tank and added a coral colony, but adding a frag or two wouldn't do it. Plus, I'd want to feed the coral to keep my bacteria population up.
I don't do corals first for a similar reason. I want to add something that's going to keep the cycle going and keep my bacteria population up. Then when things settle in a bit and there's some balance, I'll add corals. If you're adding softies, they're generally much more forgiving so you'd probably be fine but I have only LPS and a few SPS (tank is still new, will acquire a lot more SPS) so I tread a bit lighter and make sure things are semi-stable first. I say "œsemi-stable" because it takes a very long time for things to become truly stable which is well after adding fish, coral, etc. We're talking a year or more depending on the coral you're keeping, the rock you started with, etc.
I've done it many different ways though and haven't really had issues with any of them. The first tank I set up a decade ago, I used live rock, let the tank cycle from the die off, once cycled added a CUC and a coral shortly after, then a fish a couple weeks after that. It also worked out just fine.
I guess what I'm saying is, I have my own method that works for me and makes sense to me, but I've done it various ways and haven't had issues so do what you feel makes sense and what you want and feel free to experiment a bit. I think you'll be fine either way.
My only real warning would be, if you add the CUC first, make sure you have some nori or something to feed them if they make quick work of any algae. Without a nutrient source, the algae will not keep growing after it's been eaten.