There's sooooo very much more to it than what's the "quickest"...
Do you already have experience with a particular product?
Does your plant already have an installed base?
What kind of local support do you have for that product?
What is the scope of your project?
What other technologies might you need to interface with? (e.g., scales, alarm systems, printers, pagers, etc...)
"Cheapest" and "Easiest" is rarely "Best"