The only variant to avoid at all costs is lawyers' fees, which is a possessive form in which the apostrophe is wrongly omitted. Some will argue that the plural lawyers is simply used in an attributive way, but it is unusual in English to use attributives in the plural. That is, if you have three sick dogs, you would say that you have a problem with dogs, not a problem with dogs. So *attorneys' fees make little sense.
In some cases, the recovery of attorneys' fees may include fees for certain services provided by a legal assistant. The only way to avoid at all costs are lawyers' fees, where the first word is a genitive adjective with the apostrophe wrongly omitted. The plural “possessive attorney fees” is just as good, and some may even prefer that term in contexts where more than one lawyer is clearly referred to. Advice, attorneys' fees, attorneys' fees, English grammar and usage, grammar, legal prose, legal writing, rules of drafting.
Although inelegant, attorneys' fees are becoming more common, presumably to avoid making a decision on the apostrophe entirely. In Cloer, for example, Judge Sotomayor used lawyers' fees to subpoena the law, but lawyers' fees otherwise. Since attorneys' fees are already an abbreviated form of the fees incurred for professional legal services, I don't think a strict distinction between one lawyer and several lawyers is justified. However, attorneys' fees are also acceptable and some prefer them if it's clear that more than one lawyer is charging for the services.
I usually use attorney fees because they seem to be more common and because they don't usually cause confusion, even if there's more than one lawyer involved. In response, one of my partners sent me a note stating that attorneys' fees can only be correct if there is only one lawyer asking for the fees. But I don't see any situation where I can use a lawyer's or a lawyer's fees, even if that's the legal expression. Chapter 38 of the Texas Code of Practice and Civil Remedies, which provides for the recovery of fees in cases of breach of contract, uses attorneys' fees.
