There are various types of revocable living trusts and which you choose depends upon your situation.

The Single Trust is generally for an unmarried person. A married person who owns assets apart from their spouse can also have a single trust for personal assets which they do not own together as married partners. This is not uncommon where a spouse may have been previously married with children from that marriage. A single trust for an unmarried person can also be a standing "prenuptial" plan prior to a later marriage, as well. Were there to be a later divorce, assets in such a trust would be exempt from property divisions of the later marriage.

The Marital Trust is for a married couple with an estate which will probably not face any future estate tax problems (ie. the smaller estate). Both husband and wife are the Trustors-Trustees-Trust Beneficiaries. After the first dies, the surviving spouse can then do as he or she pleases with the estate and its assets.

The A/B Trust is also called a "marital by-pass trust." It is one unified trust which divideds into two trusts when the first spouse dies. At the death of the first spouse, the surviving spouse transfers to the "B" trust as much of the estate as he or she pleases. Usually this is equal to the Uniform Tax Credit amount for the year of the death of the spouse. The balance of the estate is held in the surviving spouse's "A" trust. The surviving spouse can do as they please with the assets in their trust. The "B": trust assets are held for the designated heirs of the estate and may not be so liberally used. If the "B" trust creates any income, it can go to the surviving spouse (such as real estate rental income, etc.). In certain, limited instances, the surviving spouse can "invade" the "B" trust principal. This is usually limited to major medical necessity.

The Q-TIP Trust is the Qualified Terminable Interest Property trust. Similar to an A/B trust, this divides into 3 trusts. One is for the wife, one is for the husband, and the other is for special uses. One special use is to receive the stock for a closely held corporation (ie. a "C" Corp.). From this the stock can be distributed to a number of beneficiaries. This may not normally be permitted for some corporations where the stock canot be sub-divided among several heirs. It can also be an excellent vehicle in the blended marriage where the husband and wife have children each form previous marriages as well as children together. It is a kind of "yours, mine, and ours" trust arrangement.

The Q-DOT Trust is a Qualified Domestic Trust which is necessary if one spouse is not a U.S. citizen. This trust requires a U.S. citizen to be the trustee but also provides major estate tax relief to the non-U.S. citizen spouse. Without this, an international marriage can face unexpected and immediate negative estate tax consequences if the U.S. citizen spouse pre-deceases the non-U.S. citizen spouse.
The "Special Needs" Trust can be an addition to any of the above-mentioned trusts. It is not uncommon for a family to include a developmentally disabled person who is receiving government benefits. Were they to also receive an inheritance their benefits may be suspended. A special needs trust allows their intended inheritance to be held in trust with another person as the trustee and the government benefits remain uninterrupted. Assets from this trust can be liberally used to benefit the disabled beneficiary.