I recently purchased a Sigma 17-70mm F2.8-4 DC Macro and would like to hear from you guys abotu other lenses out there that are excpetional as well. So far i have nothing but good reviews for this lens.
Im new to the Sigma brand.
I can give you my estimation of the equipment you listed. But keep in mind it is my observation.
70D, T3i<----------both entry level camera bodies with the 70D being somewhat better in build.
EF-S 18-135mm f/3.5-5.6 IS STM <---------------one of the better entry level lenses for Rebel
EF-S 10-18mm <----------------no comment on this one as I have never used one
Sigma 17-70mm F2.8-4 DC Macro <----------------no comment on this one as I have never used one
EF 50mm f/1.8 <-------------------skip this lens I have tried two of my own and a few other peoples and they are very cheap
EF-S 18-135mm f/3.5-5.6 IS <-----no reason to buy this one with the one above availible
EF-S 55-250mm f/4-5.6 IS II <-----------not too bad for entry level lens
CS6, Lightroom 5.7 <------I consider these two programs absolutely necessary and would not be with out them
Both of them not either/or !
My humble opinion as usual and worth every penny spent on it.
A thought on third party lenses, Sigma, Tamron and Tokina. There are some other lesser brands out there and if you are looking at some cheap lens form one of them, it is cheap.
IMHO, Sigma, in recent years has become a real challenger to the big boys Canon and Nikon. The company changed hands and has made huge strides to quality and performance. You can still get some, however, that are really terribile.
Avoid used unless you can try it throughly.
Tamron is pretty good but behind Sigma. They have a couple lenses that are top notch and worthy of considering namley the 24-70mm f2.8 and the 70-200mm f2.8. And their 150-600mm f5-6.3 is the best buy in a super tele zoom.
I avoid Tokina simply there is no support.
One more word about Sigma is their "Art" line. They are some of the best lenses made period but they have similar price tags. Never forget Canon is the world's leader in lenses. Nobody even comes close to the lens line up that Canon has. Not Nikon, not Sigma not anybody.