For a more current response: Cargo Up-Throw is almost always your best bet.
Grab -> Cargo -> take a step or two if needed -> Jump -> Up-Throw -> Double Jump -> Profit
This leads into all kinds of followups at most percentages for almost every character. Most notably, fully charged Neutral B or FAir for a guaranteed kill in the 70~110 or so damage range. At lower damages you can usually start an UAir chain, or NAir/BAir if they DI far enough away, or maybe even regrab or UTilt or something on spacies with very low %. Either way, keeping them above you gives you a huge advantage as DK because it is very easy to beat most enemy hitboxes from below.
In some situations on some characters, Cargo FThrow can be a substitute for some similar followups, especially if you are at the ledge or make a read on their DI. However, DThrow is risky because you're missing out on a free combo (unless they're low damage and super super floaty), and most of your tech chasing options are pretty high commitment as DK unless you are confident in getting a roll read to follow up with another grab.
At very high damage you can just backthrow them (without cargo) for a guaranteed kill in most cases, especially if they DI poorly (and why wouldn't they? You've been cargoing them this whole time, so it should catch them completely offguard).
Want more info? Study how ThundeRzReiGN plays in tournament. Not only the very pinnacle of DK skill, but one of the top PM players in the world overall right now... purely using DK. He's even recently conquered what were previously thought to be "unwinnable" matchups. Dong expansion at maximum.