tjmcnamara wrote in post #11927239
Like all of the above comments, it's hard to say what's best in a generic sense. Frankly, a portrait taken with a 5DMKii, 7D, 60D, T2i can all be excellent. The differences between these are in the subtle (and some not so subtle) differences. I have the 7D and it's an excellent camera. But using it with, say, the EF-S 50-250 (~$200) vs the EF 70-200 F4/L (~$600) would render very different results.
Very different in that you get a shallower depth of field with the 70-200 at the longer focal lengths, yes. Very different in that the autofocus of the 70-200 will be quicker and more accurate, yes (although the 55-250 isn't ultra slow or anything).
Very different in terms of sharpness, contrast, detail retention, etc.? No. Yes, the 70-200 will be better, but it won't be night and day better.
The 55-250 is a lot better than you'd think, given its price point.
It used to be that there was an immense difference in the quality produced by the inexpensive lenses versus the expensive ones. But that appears to have changed in the last couple of years, with the introduction of the 18-55 IS and the 55-250 IS. Both of those are much better optically than their predecessors. The main differences between the more expensive lenses and their inexpensive brethren these days are things like depth of field control and optical quality at the extreme edges and corners. In other words, either things where getting the improvement requires putting a lot more glass into the lens (making it bigger, heavier, and more expensive to construct), or things that tend to matter only to the most critical of applications.