canon - Would the Tamron 18- 270 mm F/3.5-6.3 Di II VC PZD make a good choice as my second lens?

I have a Canon 50/f1.8. I am looking for a zoom lens. After much research, I have zeroed in two lenses as my second lens: either Tamron 18-270 mm F/3.5-6.3 Di II VC PZD or Canon EF75-300mm f/4-5.6 III USM.

I want decently sharp images, though they don't need to be very sharp.

Can anybody who has used the above offer advice? Do you have any other suggestions? My budget is around $700-800