Hi Sadie, I don't own a Caldera, I have a Jacuzzi, but I think it would be fair to say that there would be a lot more Caldera owners on this site than Hydropool. I take a lot out of that. Also, I believe that Caldera is owned by Watkins, which also owns Hot Spring, so you probably couldn't go wrong with Caldera.
The $300 is mouse nuts in the long term, go with the one you feel best about when you've wet tested. Don't buy without wet testing.
Depending on where you are, I would also look at Jacuzzi and Hot Springs / Tiger River.