Versaille fountains or no fountains?

There is no 'show' --- Fountain Show just means the fountains are running. Some of them run in the morning and some in the afternoon. IMHO the gardens are not worth visiting without the fountains running. Here was our trip a few years ago just to see the fountains (the ugly sculpture in the center was temporary and is gone)
https://janettravels.wordpress.com/2016/02/15/fountains-of-versailles-a-little-chaos/
If you go to the Chateau that day maybe pick a noonish chateau ticket and visit the gardens in the morning and then perhaps return for more in the afternoon. (you can enter the gardens twice on fountain days using different entrances)

Just my opinion, but we found the running fountains entirely underwhelming and not worth navigating the extra crowds. I’m sure there are videos online for your review. It’s no Bellagio show, since you mentioned Vegas.

The fountains do not run all day either and not all will be operating. There’s a schedule as to what fountain will be turned on at what time so you can plan your day around this. Only one fountain at a time will be turned on. From what I remember, this is due to the fact that King Louie XIV will walk from one fountain to the other so they turn the fountains on and off as he went. The plumbing to run the fountains is original so can only handle this capacity. Pretty amazing though!

Yes, the fountains when we saw them were not really a show, but rather just running. I think there was music too. Honestly I enjoyed walking the gardens at Versailles more than all the drapes and gilded ceilings of the interior room tour. Less people outside too, at least the year and month we went.

It is not true that only one fountain runs at a time -- but they do not run all day or all at the same time -- usually some are on in the morning and others in the afternoon.

There are wonderful musical garden shows as well, please see here: https://en.chateauversailles-spectacles.fr/programmation/the-musical-gardens-show_e2758

I love Versailles, inside and outside. I love the gardens, the grounds, and the Petit Trianon especially. Been going to Versailles all my life, so at least 30 times.
We went on a Fountain Day once… never again.
I agree with SusanM, they were extremely underwhelming and the gardens were jam packed with people, which i’d never seen before or since. Even when the palace is crowded, the gardens never are, unless the fountains are running. And yes, they play very loud Classical music on a bad sound system. I love Classical music, but not like that.

• Musical Garden: Tue/Wed/Thu/Fri (7/4 - 10/31; 2023)
• Musical Fountain: Sat, Sun (4/1 - 10/29, 2023), Tue (5/2 - 6/27, 2023)

It will be Musical Garden on Friday (10/27) and Musical Fountain on Saturday (10/28) during your visit.
I last visited on a musical garden day. Baroque music was playing in the background while I strolled around the vast garden on a sunny day; a magical experience for me.

We loved it at night. It was a cooler time to stroll around the gardens,the fountains were beautiful, and the music was a nice added touch. If you go to also see the chateau on the same day, do as another poster suggested and schedule a break between the two. We toured the chateau in the early afternoonn. Then we left and hung out at a restaurant on the street next to the chateau for cider and gallettes. It made a nice break so that we were not too tired to enjoy the evening.