My girlfriend (a lawyer) tells me that if I ever need a lawyer I should get the most expensive one I can afford, because price does roughly reflect quality.

And, I'd note that we have little else to go on. After all, we can't discern the quality of a given lawyer by the outcome of our particular case. Say your lawyer lost. Were they a bad lawyer, or was it simply that your case was poor? As a non-lawyer, you don't have the expertise to judge. Furthermore, lawyers won't discuss the qualifications of other lawyers for various reasons, so it's difficult to get any sort of objective ranking.