Twin rail - full elevate setup
Alpha rail - TKI/riot.
This would be my recommendation too after riding and/or observing a few setups in our group and feedback I've read on here. The Alpha and twin rails seem to favor slightly different setups.
Two friends (Including Chewy22) have 2019 twin rails with full Elevate setups. After riding one in some deep spring snow with a few crusty layers I had no complaints, and it handled great. The price tag is steep, but something about the combination of the spindles and rail profile just works. If building one, all around use sled this is the direction I would go. I have a sled with traditional Kmod twin rail paired with Elevate spindles and while it's very capable steep and deep snow sled I'm contemplating going back to stock skid with Elevate rails for a better all around sled.
One of the friends above also has a supercharged Alpha that originally had Elevate setup with stock rail skid. He hated it in anything but fresh snow. He's since changed that setup and gone to a Kmod skinny and ZRP spindles and said he likes it better all around. How much is the skid and how much the spindles I can't say. I also have a supercharged Alpha with Kmod skinny and TKI/Riot spindles. It tips side to side noticeably easier on the shop floor than his sled with the ZRP spindles, easier to hold the sled up on edge, and skis don't try to change steering angle on me when rolling it up on edge. This is a trait stock cats have had over the years that I think contributes to their stability tracking across hills in the rough. Steers easy too even with powder pro skis. However, I did fight it on the same layered snow that the Twin Rail Elevated sled went right through without fuss.
Note that Riot and Ice Age spindles have steering stops. ZRP don't. Riot spindles give 1.5" lift if I remember right.
Another friend has a stock 2022 165 Alpha HC and TKI/Riot setup. Rode it in some soft, deep snow. Nothing really technical, but it was super fun easy to ride machine in that environment.
No personal experience with the Mountainside or BMP spindles, but there's some feedback here:
https://www.snowest.com/forum/threads/mountain-side-spindles.460389/