2-of-3 is the default option for most individuals, while more complex quorums can offer additional optionality.
The goal of a multisig wallet is to create an access policy for bitcoin without single points of failure. Certain quorum sizes can help meet this goal with ease, while others cannot.
Learn: Better understand multisig quorums by reading our introductory article.
1-of-N quorums are insufficient, because if an attacker gets any one key they may be able to spend the bitcoin. Similarly, N-of-N quorums are problematic because if any one key is lost or destroyed, access to the bitcoin is also lost.
Quorums that sit in the middle of these extremes are effective at eliminating single points of failure. The least complex quorum that meets these standards is 2-of-3.
2-of-3 multisig is a very strong, practical choice to easily manage and secure large amounts of bitcoin, as long as the keys are properly protected and stored separately.
Important: Currently, Unchained offers 2-of-3 multisig quorums to all clients, while the option for other quorums is limited to clients with an Unchained Signature subscription.
3-of-5 multisig is also popular, because it offers an extra degree of protection. Even if two keys were simultaneously lost, destroyed, or stolen, the bitcoin would remain protected and accessible. This comes with a complexity tradeoff, because there are more keys that need to be managed and stored separately. Practically speaking, two separately-stored keys being affected by tragedy simultaneously isn't something most people need to be concerned about, which is why we believe 2-of-3 is generally the best option.
Other quorums are less popular, may be useful for specific business arrangements. They may also be used by someone who wants to prioritize a stronger defense against against lost access (2-of-4, 2-of-5) or against theft (3-of-4, 4-of-5) at the cost of having a weaker defense against the other threat.