So after much consideration and the help of people here (notably forum member Chas), I bought the Hot Spring Aria. Some pictures are attached.
Keeping in mind that I'm 6-feet tall, and generally favor jets that are strong to the max, and it's all subjective, here's my verdict (using grades just for the fun of it):
Overall: Happy with the choice and enjoying it very much. Had a Sundance Altamar previously and can say, it most regards, like it better. Jets aren't knock your socks off strong, but better than most. Grade: A-
Build quality: solid and nicely designed. Color display works well. Very nice lighting. Only minor gripe is the "water feature" (fountain) -- kinda goofy, but then again, I find that most of them are. Grade: A
Filtration: I didn't take the Ace system at the advice of my dealer, since it can be added later on. So far I've had no issues and think it works reasonably well for a tub that's used 4-5/week. Love the fact that the filters aren't of the flimsy paper type that break apart. Grade: A-
Comfort: This is definitely not a tub for 4 or 5 people at a time, as Hot Spring claims. 3 fit very comfortably - which my dealer was very clear to explain before I bought it. (If you want something that will hold more, consider the Envoy, which I also considered.) Pillows are fantastic. Would've liked to have arm rests in the power seat (I believe larger models have them). Absolutely love the cool down seat. Grade: A-
Neck and shoulders: the power seat jets are fantastic. Best part of the tub by far, IMHO. Grade: A
Upper back: the Moto massage is great on the lounge, which also has decent neck/shoulder jets. Power seat nice for upper back as well. Grade: A
Lower back/hips: the Moto massage is good, but for a tall person like myself doesn't really get down far enough. Other jets are good, but not great for the lower back. Best I've found so far is to sit way down and let the foot jets do the work. (In fairness, none of the tubs I tested were really great in this regard.) Grade: B-/C
Calves/thighs: the calf jets on the lounge are only pretty good. Calf jets on my old tub were much better. (I've torn calf muscles in the past and need a strong massage on them.) Could be stronger. Grade: B-
Feet: the foot jets are very nice. Just the right strength for me. Grade: A
There ya have it. Hope that's helpful to anyone considering this model for themselves. Feel free to ask any questions that might be of help.
One last word: when people here suggest that who you buy your tub from is as important as which brand you choose, I'd heed that advice. Particularly where I live, in which most dealers are more than 20 miles away. My Aria has already encountered a problem in which the temperature reading isn't matching what I'm setting it for (by +2 degrees). Not a huge deal, since I'm assuming it's either the thermostat or the display. Buy it from a stinky dealer and I'd probably have to wait weeks or months to have it fixed. My guy will be here in two days (or at least so he says!). If there's any purchase where Murphy's Law applies, it's with hot tubs. Hence the importance of a good dealer.