Any kind of coconut water, actually. I prefer Vita Coco since it's the most widely available, but I'd imagine they'll all taste similar.
Be prepared. It's definitely an acquired taste. My girlfriend developed a urinary tract infection and this is even better for you than cranberry juice. So for awhile, we had lots of it in the house. The first time I tried it I was turned off by the weak flavor, the strange oily-yet-watery texture to the liquid, and generally the whole experience.
But we had it, it cost a lot (Whole Foods, of course), and I sure as hell wasn't going to let it go to waste. So after kinda' choking it down for a few days, I found myself really growing to like it. It was super-refreshing. That oily-yet-watery texture quenched a dry throat like nothing else. The mild flavor made it easy to drink. The nutrition is tops. And the low-calorie count (5-7 calories per ounce) means you can drink lots of it and not turn into a dirigible like you would with soda. That of course assumes you can afford lots of it.
That's the other issue with it. It's pricey. It's impossible to find it for less than $1.25 per box, but Red Bull costs that much and people drink that like it's about to made illegal. Or that it's already illegal. You can buy big boxes of it, like I have in my photo, on Amazon that works out to about $1.75 per box. That's pretty much as cheap as you're going to get barring a sale.
Still, if you can swing it, it's so worth it. The health benefits are numerous, the calorie count is lower than any juice (14 per ounce for OJ), and the boxes are convenient. Unfortunately, as of this writing, the large 34-oz cartons aren't widely available, so you're stuck with the small ones whether you like it or not.
I mentioned Vita Coco, but the other big brand on Amazon is Zico. Their price ends up being pretty much the same at first, but it isn't offered under Amazon Prime, which I have, which means no free shipping, which adds a lot to the cost. Both Vita Coco and Zico can be bought in large cartons, which makes VC about $0.16 per ounce and Zico $0.10 per ounce, but none of that comes with Prime. And at $15+ for shipping, it's not viable. For example, Vita Coco becomes $0.24 per ounce.
So, in the end, it's difficult to get, expensive, and the taste can vary from box to box. Still, I heartily recommend trying coconut water. Give it a chance. Force yourself to drink a few cartons over the course of a week. I think you'll grow to like it.