If your looking for cards to explicitly feed the next in either case, you're playing bad Magic, because you're just drawing cards to help you draw more cards.
Treasure Cruise and Dig don't NEED to be delved for the full amount I'll often gladly pay 2-3 mana for a Cruise to avoid hitting my own Goyf of Snapcaster.
The reason Cruise feeds better is that each card you draw either stays on the battlefield and helps you win, or goes in the graveyard. The "But what if lands?" argument is invalid, because there are times you'll want to get lands with Dig.
Dig is only better when the power level of cards in your deck varies greatly due to synergy, such as combo plays, or due to availability, such as limited and Standard because the smaller card pool doesn't allow for card quality equity. In limited and Standard, the quality disparity between any two given cards in your deck is going to be far greater than the quality disparity between any two given cards in a Modern, Legacy, Vintage deck, which causes Dig to be ultimately better in these formats.
However, my statement wasn't directed at Standard, I was talking Legacy, but it's true of Modern and Vintage too. In any deck with a relatively flat power level of cards played, which is true in most "fair" decks in larger formats, i.e. Vintage, Legacy, and Modern, Cruise is far better because it doesn't matter so much what you're drawing, but just that you're drawing more stuff.
For instance: When playing a Delver deck, Dig will always hit the two cards you need. You will rarely play a turn with no action so we can assume that the Delver player already has 3+ lands, if you're casting Dig Through Time. In this case, Dig will always get you two live cards.
When playing the same Delver deck, Treasure Cruise will, rather than getting the 2 cards you need, get you any 3 cards. I understand, this often sounds worse, but, when you just need to stay ahead of the opponent, this is much better. it keeps you out of top-decking, you'll often hit 2 live cards anyway, since the cards power level in your deck is relatively flat, and approx. 2/3s of your deck isn't land.
Ultimately, it boils down to Dig being better in smaller formats, synergistic decks, and the fact that it feels stronger when your game is going well, but Treasure Cruise is the much safer lock on the game, because it provides more raw card advantage.
I'm not saying Cruise is always the better of the two cards. I'm saying that different decks/formats will want different cards, and most fair decks in large formats should probably opt for Cruise, even though Dig is the stronger effect.