Originally Posted by DannoXYZ
Personally I would do both if you can because they are different tests. LT is for muscular-exertion and VO2-max is for aerobic-capacity. Having both sets of data and being able to graph relative to HR will give tremendous insight. However, as previously mentioned, you can test LT out in the field while VO2-max requires a lab. So if you can only do one, do the VO2-max first. While it does improve slightly with training, it doesn't increase anywhere nearly as dramatic as power-at-LT and muscle-efficiency (power per O2 consumed).
I prefer to think of VO2Max as the size of one's engine and LT as the governor on that engine. With the proper training, the governor's setting can be set higher without "blowing up" and will be a greater percentage of what your engine is capable of yielding.
IMHO, LT @ power (watts)/kg of body weight is the best metric, but only if you can make measurements on a regular basis. A single measurement (of either) is of no value.