If you're at the point where a riffle shuffle is a challenge, I recommend sticking with inexpensive decks like Bicycle Standards.
Here's the thing about custom decks - The vast majority are printed by the USPCC. That means, despite what the Kickstarter campaigns and such may say, they're all pretty much the same. There just isn't that much variation in what they will print. Most of them are either the standard Air Cushion finish, and casino grade stock. So what you're paying for is the art work.
To that end, look at the designs on offer and see if you're willing to pay what they are asking for.
There are exceptions, of course. Legends Playing Cards (I think that's the right name) have a different stock and finish to them. They almost feel oily to me when they are new. But they are workhorse decks (I have some of the Gnostic deck by Stuart Palm). There's also the Fournier decks, which are I believe varnished, and I am told feel totally different to USPCC cards.
But as I said - when you're at the point you're at, you're going to be destroying decks just by practicing. Unless you're making money from magic or flourishing, or just have that much disposable income, I personally would avoid using expensive decks.