Rekordbox is cool but the problem is that the pioneer hardware that runs it isn't compatible with Serato so unless RB becomes industry standard then I think its pointless
I have actually been playing around with RB and it does everything you need it to do but sometimes it does feel very heavy while its running, maybe its my machine but I do sense a bit of lag in the program, otherwise, there are no other complaints programmatically The ONLY other thing to take note of as something has already mentioned is that RB is ONLY paired to PIONEER controllers/mixers, so if you are planning to keep using it, you will have to walk with your own hardware to gigs. My 2 schillings
Rekordbox has some nice features which Serato DJ doesn't or didn't. With the new Serato DJ Pro there have been features introduced that only RekordBox had before. Nevertheless i would say that RekordBox is ahead of Serato DJ when you compare the features and the library management. But when it comes to stability i would still prefer Serato DJ. But since Pioneer is bringing out lots of new hardware which is RekordBox you should definitely check it out