- page render time server side
- time until the user sees something meaningful (you ought to be able to measure this with a headless browser if you have some idea what the first thing you want the user sees) This will get you what people might think they're getting out of the TTFB metric.
- full page load latency
- data transfer latency
TTFB might be useful if you have some data that suggests your web server is a significant bottleneck, but I wouldn't gather it as a matter of course in trying to optimize page load times.