Hey Soup,
Sorry if I'm late to the party, but I thought I'd chime in since I've spent the past two years searching for the perfect shuffle stack.
While much of this comes down to personal preference, I would say that only applies after a certain point. As in, you're definitely going to want to get Paulson's, but what kind of Paulson's can be up for debate. I'd recommend not even wasting time or energy on any of that Chinese crap, as it'll just draw out the process of finding something that you'll really enjoy shuffling.
Once you're looking at Paulson's, then it gets into THC vs RHC, leaded vs non-leaded, 39mm vs 43mm, but overall I'd say a great safe bet would be the inlay Paris $1's. You can get a barrel cheap enough and they will be newer THC's, once you break them in a little, I think for the money this is probably the best bet.
If you were looking to go a bit beyond, this is where you start to enter the land of lead and butter. In this category, I'd recommend something like Lakeside Inn or Harrah's. Because of their age, many of them have been worn to perfection and shuffle like butter. Also, the added weight from the lead gives them a satisfying punch.
Now, if you really wanted to reach for the top, the best shuffle stack I have found has to be the gargantuan, heavy-leaded, 43mm Garden City $500's. Not only are they worn enough to be smooth like butter, but they shuffle like hockey pucks. They are so large and heavy that you can feel and hear each one stack onto the other in a numbingly blissful symphony of chipping beauty.
A shuffle stack can be a tricky thing, and even two barrels from the same casino can age and wear at different speeds so they won't all be the same. But as long as you stick with Paulson's, you can't really go too far wrong. Everyone will say it's a matter of preference, like choosing a flavor of ice-cream. But just remember, you want to be choosing from a curated selection at Baskin Robbin's, not scavenging their dumpster for China Clays.