I did both, though only a 1 year rotation in tax. My take is that tax is more interesting work. I found it more intellectual, more research, and less process or just ploughing through steps on a checklist. The problem is that your expertise gets deeper, but narrows as you progress. So you because much more valuable, but to a smaller group of people. So your jobs are more stable, the pay very well, but the upside is much more limited.

So if you are a reasonably smart tax person that is hard working, there is a very strong chance you will be making at least $150K in 10 years or so, and very good chance of making $200K+ or so. Also, making partners is still more difficult, but if you can create a profitable practice, it is much easier than in audit (where it is very difficult to win big new audit clients).

But another thing that sucks is that much of the tax advisory business is handled by law firms. So as you progress upwards, you have competition with tax lawyers and many of the tax consulting areas at tax consulting firms and the Big 4 are inundated with lawyers. So you might hit a glass ceiling there as well.

As for audit, simply there are much, much more jobs available on the outside. Every organization needs internal accountants and Big 4 alums progress really well. The outside businesses don't have a huge need for tax accountants, because it is easier to outsource that function to outside firms. The other things about audit, is that you are exposed to business operations and business processes much more, and aren't so focused on GAAP or IRS rules day to day. So not only can you get into an accounting department, it isn't as big of a stretch to get into other fields within business. A lot of IT and finance executives started as auditors. I would say the downside is that as an auditor, if you don't work hard or aren't particularly bright, it is a lot harder to get promoted upwards and it is easier to get stuck in a rut.