Best discone?
Not sure about best, but you can do better than the consumer/amateur grade stuff. But, it's going to cost you.
$1600.00:
I use that one at work. Most of the time it's connected to a frequency agile remote controlled receiver. But, in a pinch, I can use it with any of the repeaters I have at the site.
There are better/more expensive ones.
I've got a Diamond I scored for free many years back. It's been up on my roof at home for many years, mainly connected to a Motorola CDM750. Fed with decent coax, it's an OK antenna. Hasn't fallen apart like some of them do.
Key is to install it correctly.