Why do the quantitative results for the same lens vary from reviewer to reviewer? And how can I make expensive purchases as an informed consumer?

Preface: Obviously, I know you can't take good photos by buying a bunch of expensive equipment alone. But I consider myself a frugal person and I'd like to have the power to buy the "best" lens for the $$$ out of principle.I think I've been relying on the particulars of individual MTF (resolution) charts too much; while one shouldn't inter-compare between camera bodies/chart types as far as the absolute values are concerned, I used to think the relative resolution/chromatic aberration values would be consistent between apertures, centers/edges of frame, and focal length, no matter the reviewer. However that seems to be the case only sometimes. For example:Nikon 14-24mm f/2.8, photozone: big center-edge differences, not very goood at f2.8@24mm, chromatic aberrations twice as bad (but still correctable)Nikon 14-24mm f/2.8, ephotozine: good everywhereIf I'm making a purchase decision, the first result tells me "the tamron 15-30mm is about as good" (reviews for that are pretty consistent), the second tells me, "no, the 14-24mm is better".So... how can I make informed decisions when there is this ambiguity? Are there reviewers I should trust more? Are there manufacturers that I should trust to make more reliable/consistent lenses (for example, maybe Sigma sends reviewers the good ones, but they make a lot more lemons)? via /r/photography http://ift.tt/2tTU1S5