They don't have a direct comparison, but you can check out their individual reviews for each.
FYI ... I had very high hopes for the 120-400 ... but it is just too soft for my taste.
See also www.slrgear.com
NOTE: the 80-400 is an APO design ... the others are NOT.
I highly recommend the 100-300 f4 APO EX DG HSM (sadly no OS, but a full stop faster at the long end & plays really nice with the matching 1.4x). I shot it on a D70s and am looking for a replacement for it in a Canon mount. As such, I have considered all the offerings in this range, with the Canon 100-400L being quicker AF & having IS. THe Tamron 200-500 is very slow although it seemed to have pretty good IQ (shop testing).
Other FM users have indicated the 150-500 falls apart after 400 ... tests show the same ... otherwise, the 150-500 had been on my short list.
You didn't mention which mount, but if you are looking at Canon the 70-300 IS is very good albeit not as quick to AF as the 100-400L ... but about $800 less on the used market. If I get tired of looking for my Sigma 100-300 f4 APO EX DG ... I may 'settle' for the 70-300 IS and accept the slower aperture & slower AF ... keeping IQ
I haven't tested any of the Nikon's ... but SLRGEAR is pretty high on the xx-300 VR.
FWIW ... I'll take the shorter lens (i.e. 300 shooting around 275-280) with better rez and crop rather than longer and soft.
