There are a substantial number of photographers who simply MUST have the "latest and greatest".
The camera manufacturers, of course, LOVE these people!
I know many photographers who buy a new body every two years! (More money than brains?)
Every manufacturer is constantly introducing new models, and any one model is lucky
if it lasts even two years on the market before it is superseded by its successor.
I'm sure it must bother all of the other manufacturers that the current reigning "king of cameras"
is made by Sony (at least for a few months).
I have two DSLR bodies. Of the 336 cameras tested by
www.dxomark.com,
one of mine gets a score of 86 and is #33 on their list.
The other one gets a score of 83 and is #44 on their list.
I consider that to be "respectable".
Some people earlier in this thread got quite "testy" when I suppose they discovered
that their camera wasn't high on the list.
If that sets you off, then for sure don't start exploring the over eleven thousand lenses
they have tested and given ratings. The best lens (a Sigma) gets a score of 51 on a
floating scale. The worst lenses get a score of only 6.
The median average (exactly in the middle of the list) is a mediocre 16.
In general, prime lenses score much higher than zoom lenses.
Sorry to burst your bubble, my enthusiastic friend.
If you go to the website
www.dxomark.com which independently rates camera sensor image quality (and also lenses)
you will discover that they have tested 336 cameras.
Of the top fifteen cameras they have tested and ranked there are six Nikons-
in positions 2 (score 97), 5 (score 96), 7 (score 95), 8 (score 94), 9 (score 94) and 10 (score 93).
Sadly there is only one Canon (the 5D Mark IV) in position #15 with a score of 91.
By the way, the current top ranked camera is the Sony A7R II in position #1 with a score of 98.
If you go to the website
www.dxomark.com they have tested both of these lenses.
Depending on which version of the 18 to 270 mm you have (and what camera you are using it on) it gets a score of 10 or 11 or 13 (more or less out of 50).
The 16 to 300 mm, with the same variables, gets a score of 12 or 17 (also more or less out of 50).
In summary, neither of them are great lenses, but the newer lens is slightly better than the older lens.