Wharf is, bar none, the best card-drawer in the game.
And on some level, that's what you need to know. Card drawing is valuable. Wharf is the best one. It works well in all the cases that you want to draw cards. It excels, paired with a village-type card, in a cards/actions engine. It is also extremely good, bought in moderation, with a big money deck, or practically any other deck. As a terminal, it should be bought somewhat sparingly if you do not have a village-type card. And that's pretty much how card-drawers work in Dominion.
But it may be a bit surprising that Wharf is the best card drawer in the game. It, after all, gives only +2 Cards, in the same category as such low-tier terminal drawers such as Witch, Steward, and Vault (all of which are good cards, mind you, but not principally due to their ability to draw cards). Of course, Wharf gives you the +2 Cards effect twice, but the general rule in Dominion is that one big turn counts more than two little turns, so you might imagine that Smithy, with its +3 Cards now, would beat Wharf, with its +4 Cards split up in two.
As it turns out, however, the +2 now/+2 later dynamic really works, and is, especially in a cards/action engine, perhaps better than a single massive draw, like you'd get with Council Room or Envoy. If you're building an engine, what you really want is consistency. It's easy to build an engine that sometimes draws your entire deck with 6 cards to spare, and other times stalls out instantly. Village/Wharf engines are substantially less likely to do that than any other two-card engine. The action economy of Wharf, and its consistency across turns, allows you to MUCH better weather turns when Villages are sparse in the top of your deck, and leaving several Wharves out each turn effectively lowers the size of your deck, increasing the density of the Actions you want to play next turn. Nothing cures the deck-stalling blues like using Wharf as your card-drawer, and no two-card engine will remain powerful longer during the greening phase than village/wharf.
And, speaking of buying greens, the one thing that you always want with a cards/actions engine is +buy to let you catch up with faster-to-accelerate but lower top-speed decks like Big Money. Convenient, then that Wharf gives you that built right in to your engine, which enables you to both often buy multiple engine components in the early-mid game, and then catch up on greens in the late game, without costly diversions to buy a Market, Hamlet, Pawn, Festival or even (shudder) a Woodcutter or Herbalist.
Indeed, the draw of Wharf is so powerful that you can more-or-less make it work with even the +2 Actions/no cards village variants such as Festival, University, or Shanty Town. University arguably makes up for its lack of +Cards by enabling Wharf draws, but these engines are certainly more prone to stalling and failing than a vanilla Village/Wharf engine. Still, Wharf is powerful enough that, given a decent board, they can still be victorious in a way that, say, Shanty Town/Smithy never could be.
How good is a Village/Wharf engine? It's so good that Village/Wharf, with no other enablers, can completely stomp Big Money Ultimate on a Province board, a distinction it shares only with (to my knowledge) Village/Torturer. In fact, this simple Village/Wharf engine also beats BMU + 1 Wharf, which is quite a high bar. It utterly destroys BMU, 77-20-3. (Notably, in Province games without other enablers, other BMU variants may beat all but the best-made Village/Wharf engines, such as BMU + 2 Wharves. But that's the nature of engines in Province games, and the built-in +buy of Wharf does mean that when anything even vaguely enabling is on the board, you can pick it up pretty easily).
<player name="Village/Wharf Simple">
<buy name="Province"/>
<buy name="Duchy">
<condition>
<left type="countCardsInSupply" attribute="Province"/>
<operator type="smallerOrEqualThan" />
<right type="constant" attribute="3.0"/>
</condition>
</buy>
<buy name="Estate">
<condition>
<left type="countCardsInSupply" attribute="Province"/>
<operator type="smallerOrEqualThan" />
<right type="constant" attribute="2.0"/>
</condition>
</buy>
<buy name="Wharf">
<condition>
<left type="countCardsInDeck" attribute="Wharf"/>
<operator type="equalTo" />
<right type="constant" attribute="0.0"/>
</condition>
</buy>
<buy name="Gold">
<condition>
<left type="countCardsInDeck" attribute="Gold"/>
<operator type="smallerThan" />
<right type="constant" attribute="2.0"/>
</condition>
</buy>
<buy name="Wharf">
<condition>
<left type="countCardsInDeck" attribute="Wharf"/>
<operator type="smallerOrEqualThan" />
<right type="countCardTypeInDeck" attribute="Village"/>
<extra_operation type="plus" attribute="3.0" />
</condition>
</buy>
<buy name="Village">
<condition>
<left type="countCardsInDeck" attribute="Village"/>
<operator type="smallerThan" />
<right type="countCardsInDeck" attribute="Wharf"/>
<extra_operation type="minus" attribute="1.0" />
</condition>
</buy>
<buy name="Gold"/>
<buy name="Silver"/>
</player>
When not paired with a Village, well, Wharf is still a terminal. It's a good terminal, and +cards is welcome in pretty much any kind of deck, but you can't flood your deck with it. Its Duration effect means you can buy a few more Wharves than you otherwise would -- 2 Wharves + BMU beats 1 Wharf + BMU, but a third Wharf doesn't help any (neither does it hurt). In a non-Village situation, it's a strong terminal that doesn't require a lot of strategy to play.
Getting back to the central claim of this article: Wharf is the best card drawer in the game. By that, I mean that it is the best card drawer qua card drawer. Torturer will usually beat it as a compliment to Village if your opponent can't deal with the attack of the Torturer, certainly, but Wharf will allow you to more consistently draw your deck. Council Room is the only card that challenges Wharf's supremacy in terms of allowing you to draw, but the advantage it gives to your opponents is potent. Council Rooms paired with Militia or Goons will tend to beat out Wharf, however -- +4 Cards in one turn is better than +4 Cards over two turns, if Council Room's singular disadvantage can be ignored.
The final verdict: Wharf is one of the best all-round cards in the game. There are hardly any boards on which it should be ignored, and if there is a Village-type card in the game, it is likely that Wharf will dominate the game and its supply pile will be bought out.