Off the top of my head (and going by memory). I know little about her apart from a few decisions and a couple of quoted speeches. The statements made at a few public appearances are troubling.
Beats Harriet Myers in the qualifications department, but no one else in recent memory. Sufficiently qualified by experience, but I would have prefered a bit beefier resume. The other two people mentioned as under consideration -- Diane Wood, Elena Kagan -- would have similar judicial leanings, but appear to be better qualified and have less strong beliefs about making policy from the bench.
So Clarence Thomas isn't "in recent memory" then? I also don't necessarily agree that Dean Kagan is "better qualified" than Judge Sotomayor - she has a "beefier resume," I think, but she has never been a judge. So really, it depends on what you look at, I think. I wouldn't say either one is definitively "better qualified" than the other.
As far as time on the federal bench goes, I believe Sotomayor has as much or more than any nominee in recent memory. Not that experience on the federal bench is everything, but it's something to look at.
For reference:
Judge Sotomayor:
ADA for New York County.
7 yrs. at Pavia & Harcourt.
6 yrs. Judge for S.D.N.Y.
10 yrs. Judge on the Second Circuit.
Judge Wood:
Clerk for Judge Goldberg of the Fifth Circuit.
Clerk for Justice Blackmun.
1 yr. at Office of the Legal Adviser for State Dept.
1 yr. prof. at Georgetown Law.
14 yrs. prof. at U. of Chicago Law.
13 yrs. Judge on the Seventh Circuit.
Dean Kagan:
Law clerk for Judge Abner Mikva of the D.C. Circuit.
Law clerk for Justice Marshall.
2 yrs. at Williams & Connolly.
4 yrs. as law prof. at University of Chicago Law.
Assoc. White House Counsel
Deputy Asst. to the Pres. for Domestic Policy
Deputy director of the Domestic Policy Council
4 yrs. as law prof. at Harvard Law.
6 yrs. Dean of Harvard Law.
Solicitor General
Harriet Miers:
Law clerk for Judge Estes of N.D. Tex.
29 yrs. at Locke, Liddell, and Sapp.
General Counsel for Tex. Gov. G.W. Bush's transition team.
Personal lawyer for Bush.
Asst. to the Pres. and Staff Secretary.
Deputy Chief of Staff for Policy
White House Counsel
Justice Thomas:
Asst. AG of Missouri
Atty. for Monsanto
Legislative asst. for Sen. John Danforth
1 yr. at the Dept. of Education
8 yrs. Chair of the EEOC.
2 yrs. Judge on the D.C. Circuit