如何選鏡頭選擇？

一鏡走天涯,
PROS : one lens do all, less gear, less bulky.
CONS : quality sacrifice ... quality dropped ...
I have tried 18-200 tamron and 18-200 sigma ... both cannot satisfy me ...
and I do landscape more, so I need something wider ...
when it for zoom ... you need those f/2.8 L lens ... above 200-300mm and IS/USM ...
if you need a traveller lens, 18-200 is good to go ...
sigma or tamron your choice ...