Canon 55-250 IS vs. 70-300 IS
Get the 55-250mm IS. It's a decent lens for what you're doing. I bought one several months ago and have had no regrets. The butterfly picture was taken handheld, with a Canon Speedlite 320EX to fill in the shadows.
Thanks for all of your replies. It seems that many are happy with both of these lenses and there's not a whole lot of bad things to say about them.
I'll probably get the 55-250----what the 55-250 has going for it for me is:
1) Smaller / lighter
2) Only $100 (vs $300 for the 70-300 IS) (these are the prices I'm getting because of rebates)
3) Better minimum focusing distance for "macro" (1:3).
Looks like the 70-300 IS might be sharper in the longer end, but I'm not sure how significant that will be for my use (daytime use: for occasional outdoor wildlife in my backyard, the trip to the zoo, or taking photos of family outdoors from a distance).
I could always spend the $200 toward another lens in the future in the lower FL's that I'll be using more.