Thank you everyone for the great feedback. I am still finding my niche in the photography world and shoot a wide variety of subjects. I do many indoor shoots with infants and maternity clients (with lighting equipment) in the close quarters of their homes and outdoor shoots for most of my other clients (seniors, couples, families, children, some maternity and headshots) I will be shooting my first wedding for a friend this summer and wanted to upgrade to a versatile lens that would last and could work for many of my shoots. My budget for gear consists of the number of shoots I book and as you all know, it's very hard to find a great lens within a small budget. I am using an EFS 18-55 mainly and an EF 50. I also have an EF 75-300 that rarely gets used. They are all kit lenses and I've pushed them as far as they can go. My images aren't sharp enough and I am spending far too long in PS trying to fix that.
I am leaning towards paying the extra and buying it new just so I will have a full warranty and peace of mind that I know I bought new and I didn't buy a refurbished lens that went through a traumatic experience. Though I have been given many recommendations of credible refurbished canon dealers, so I may have to look into that. I found a great lens rental service but I'd much rather save the extra money towards purchasing this lens which is why I am asking for your reviews.
Up should spend some time working with that 75-300 for portraits. Try it at 85, 100, 135, 200 and see how you like it. (I say this because, there seem to be lots of big names that use the 70-200mm as their portrait "go-to" lens).
There is a world of difference in IQ between the 75-300 and the 70-200. The 24-105 has excellent IQ, but is a bit on the slow side, f4, for my tastes and needs.