I'm going to a top 20 law school. Simply put, would you recommend taking a job with a BigLaw firm or is the workload/stress (especially, say, after 5 years or so) not worth it?

I take it you're not yet attending "a top 20 law school."

Simply put, YES, you should take a job with as prestigious a biglaw firm as possible (while also bearing in mind whether the firm is strong in your intended practice areas, is prominent in your desired geographic area(s), etc.).

If, once the honeymoon is over, you find the hours (due to the fact that you are being paid top dollar, at least in the early years, mainly for your unfettered availability) too oppressive, you can seek employment: (i) at a smaller firm (e.g., at one of the premium midsize firms with minimum hours expectations of around 1850, rather than 2000); (ii) in-house; (iii) with the government; (iv) depending on your practice area, start your own practice (or form a firm with another biglaw refugee or two); (v) with a public interest entity; or (vi) if you're the editor of your school's law review and you do a federal clerkship, as a law professor (though certainly not at a top 20 school). Note that most of the above are considered "exit options" for a reason: they are options enjoyed only, with but rare exceptions, by biglaw associates.

Name a path other than biglaw. You can be sure that, whatever it is, not only would that path remain open to you after your stint in biglaw - it would most likely be MORE open to you. Premium midsize (i.e., not insurance defense sweatshops) and boutiques generally hire laterals straight from biglaw; in-house, especially at top companies, hire straight from biglaw; top government jobs (e.g. U.S. Attorneys, agency counsel, etc.) hire (mostly) from biglaw; and even many of the best public interest gigs (e.g., ACLU, Aspen Institute, WWF, Nature Conservancy, Amnesty, etc.) also look to biglaw.

There is a lot of blather pre-law school and during the first year of law school as to whether to seek a "biglaw" job or a "small or midsize firm." Guess how many hours new attorneys at most small or midsize firms are expected to bill? In most cases, it's the same as it is at the biglaw offices in that market. The differences are that you will be paid half the money to do so, in a less attractive office, with a less valuable addition to your resume, and with no head hunters calling you. In the second and third years of law school, there is further talk such as "I never wanted to work at a big firm anyway." Decide for yourself the validity and honesty of such views.

If nothing else, why in the world would you pass up a chance to have the BEST job in the professional world (mainstream professions, i.e., excluding sports, entertainment, etc.)? What job is that? Two words: summer associate. For three months, you are paid at a first year associate's salary, just to amble in at 9ish, do a little work (which is often more interesting than what junior associates get), be taken lunch at the best places in town, return to the office and either do a little more work, attend some interesting presentation, sit in on a conference call among partners and clients, and then stroll out by 5ish (perhaps then attending a lavish happy hour or being taken out to dinner). Such a typical day would be disrupted only by attending a baseball game, taking a tour or taking in some other major attraction in the city. Three months of that, all while being treating like a prince or princess by (most of) the associates and partners at the firm.

I couldn't agree more. Taking a biglaw gig right out of school is a no brainer if available. The only exception would be for a prestigious clerkship, followed by a stint in biglaw. It's amazing how quickly people move onto their second job. I'm an 05' and half of my peers are already at their second job. Also, people skate by at biglaw sweatshops billing 1600 hours for a year or so.