Okay.. So my tub is a standalone. So I am biased. However-- There are two use cases for a hot tub, and depending on what those are, then your decision will be different..
Where standalone is better: When you are using the tub for therapeutic uses or just relaxing and can take turns with the other people in family and/or guests using it. Having it standalone is MUCH better in the winter (even here in Tucson) as it doesn't take 45 minutes to heat up and use $25 worth of natural gas in the process. Even new, it's less than 1/2 the cost of built-in. Even with electric heat, a decent tub is MUCH more energy efficient, and again is much more useable in the winter, when you really want to use one. They tend to hold less people than the manufacturers state and you do have two sets of water chemistry that often act a lot differently to deal with for TFP.
Where built in is better: When done for aesthetics, or for someone who entertains a lot and expects to have a big number of people in the tub often. I have not been in one that is comfortable for relaxing or therapeutic uses, and I have been in many. They tend to be energy hogs, and they also aerate the water a lot, which can be good or bad depending on the circumstances. There is more equipment to buy and use the built in and because of that it's +$15K-25K to add one to a pool build. There is no good way to insulate the tub, so it's inefficient in that regard as well. Again, there is going to be much fewer features and nozzles as stated above...
If I had it to do all over again, I'd still do the standalone... maybe one size bigger, with a few more bells and whistles... but I don't regret that I didn't build in the spa at all.