Depends on the bike, as in what you're replacing. The '15 RSV4 has an upgraded OEM Brembo, and couldn't possibly be any better. Same with the '15 BMW (unlike the earlier models). On the earlier bikes, it would be a worthwhile upgrade. It would be particularly useful on, say a Gen 4 ('11 - '15) ZX10R, where the stock brakes were pretty poor. If you'd just bought the 2016 ZX10R, you'd be unlikely to notice a large benefit.

In descending order of importance to braking performance, I reckon it goes something like:
40% pads
25% M/C
20% discs
10% fluid
5% lines