That was only an issue with the DOS-bootstrapped versions. The NT line was a lot more reliable for early adopters. Or at least it was until XP came along. Which is another good reason why Microsoft peaked with Windows 2000.
I think that there were several different peaks. In terms of UI, I'd say Chicago is the peak. In terms of internals, you're probably right, it was 2000. In terms of performance, I'd say it was probably Windows 7? Maybe it was just because I actually put together my own tower instead of pre-built?
UI is subjective. Performance, however, 2000 was again the peak there. It was the first desktop OS that supported SMP (obviously not the first workstation OS. But I'd argue Windows 2000 was a cross-over platform that brought workstation stability and performance to desktops).
Also look at the era: OSX wasn't yet released and Mac OS 9 was a tire fire (worse than Windows 98). Windows ME was somehow worse than Mac OS 9. BeOS was awesome but pretty much a failed company by that point plus lacked a lot of software one needs day to day. And Linux was pretty buggy as a desktop -- usable but a long way from being polished. Windows 2000 wasn't just a good OS by it's own standards of the hardware at the time. It was an incredible OS by the standards of everything else available at the time.
By contrast, when Windows 7 was released, Linux was still faster and had several well polished desktop environments by that time. FreeBSD made a decent desktop too. OSX was in its prime. Windows 7 was only good by comparison of what it followed: Vista. But it was a long way from competing with the competition on anything bar AAA game support.