I would say Wyoming benefits the most as it is the least populous state but one member of it's three member delegation has near equal power to one member of California's 55 member delegation. The delegation in full will be elected by the same group of people (as will any state with a three member delegation), so they will usually be close in political thought. This means, that in effect, all Wyoming will have a more monolithic power and will be able to vote on something with three times the representative power of per number of delegates of states with 4 or more members of the delegation more often. This is true of other 3 delegate member states, but as they represent the same ~500,000. Wyoming will effectively have the voting force of ~150,000 in all issues where the deligation is in agreement, giving them the most power for the least amount of citizens. Meanwhile, where California's sentators will likely be a monolith representing nearly 80 million voting force combined, their House side is decidedly purple so that combined force can will in theory vote with a force of ~160 million, but will rarely reach that because it has significant opposition party votes, so the true force is much smaller.
This really doesn't matter in the legislature so much as the presidential. Assume a situation where:
- The election in each state is so close, that each candidate wins by one vote in the states they win
- The winning candidate wins by the smallest possible margin of electoral college voters, such that they win enough to get to 270 and over by the last state to create the win.
- Washington D.C. is included.
In a possible scenario where the victor candidate wins by taking only the largest possible states by population, and in every race he either wins by one vote or loses by one vote, then the candidate becomes the President with only 22% of the popular vote.
In a possible scenario where the victor candidate wins by taking only the smallest states possible by population, and in ever race he either wins by one vote or loses by one vote, then the candidate becomes the President with only 21% of the popular vote (the winner takes D.C.).
Therefor, because of the slight advantage in the Presidential races, and the more unified nature of the delegate votes, the compromise slightly favors small states in the extremes. As Wyoming is the smallest state in both scenarios by population (including Washington D.C., which has no voting representation in congress and still is slightly more populous than Wyoming) it stands to reason that Wyoming has the most power per capita of any state, thus is the biggest beneficiary of the Great Compromise.