In my opinion, Krookodile all the way.
Now let me explain, when playing Pokémon White, I’ve used both of them, at different times though, but I can say Krookodile is much better.
First, Krookodile has moxie, which make him incredibly strong as a Sweeper. If you’re playing BW, he should be able to decimate Caitlyn’s and Shaunta’s team alone.
Krookodile has very nice attack and speed, and has access to coverage moves like Rock Slide, Aerial Ace and even Outrage.
Krookodile is also easily available, you can get Sandile early when leaving Castelia city, while you’ll have to wait more to get Joltik.
So here’s a nice moveset you can try on Krookodile, which I used myself in White.
Ability :- Moxie
Earthquake - STAB move, high power and accuracy. Bulldoze is nice too, but has a lower power and lowering opponent’s speed is not necessary for Krookodile since he already has high speed.
Crunch/Foul play - Choose whichever you want, Foul Play can be good if the opponent has high attack,but this isn’t really reliable Ingame. Crunch is safer and has a chance of lowering Defense.
Rock Slide - Coverage move for Krookodile, and has a chance to make the opponent flinch, and can be paired with King’s Rock. I think it’s better than Stone Edge, since you’re playing Ingame and PPs as well as accuracy are a great factor.
Outrage - Just a filler move, but can do tremendous damage to an opponent who happens to resist Krookodile.
All the best :)