real McCoy

the real McCoy (if someting is described as the real McCoy the it's the real thing, it's not a copy or a fake, therefore it's probably the best; a genuine item)
1. мировой парень; парень что надо; мировая девчонка, и. т. п.
2. подлинный, неподдельный, настоящий
3. "классная штука"

1. At least her boyfriend is the real McCoy. —Её дружок — мировой парень.

2. This painting was the only real McCoy. — Эта картина была единственным подлинником.

3. At Mary's wedding we drank the most beautiful champagne. You could tell it was the real McCoy (It was real champagne from France). — ...Чувствовалось, что шампанское было самое настоящее французское.

see also
the biggest/best/nicest etc something going (the biggest, best etc of a particular thing):

...It's some of the best beer going.

...It's got to be the best ticket office going.

....Perhaps the biggest thing going was the harp played by JoAnn Turovsky, sounding positively, well, huge.

[what the doctor ordered]
[bee's knees]