You definitely need to have live demos of each system, using your specific assembly if you want to compare apples to apples.
Each of the AOI OEM's you mentioned have plus amd minus to their unique systems. You will need to evaluate your specific needs, what attributes are super critical to your success and any compromises you are willing to accept.
Are you price sensitive first? Or do the actual technology and end results become primary considerations.
It's been nearly 3 years since I've conducted an in-depth study of AOI so I cannot advise on current offerings. I will say that I was most impressed by MVT at that time. I liked the 3 color LED array they used for a lighting source. Others use gray scale imaging, which in my opinion was limiting and caused too much operator/engineer intervention to make a go/ no go decision on the spot. I understand that MVT has since been purchased by a large organization and some of the desirable flexibility in custom tailoring the application software may not now be available.
What will be your intended use of the AOI? will you conduct post print inspections? pre-reflow inspections for correct part, orientation, alignment, presence/abscence?
Will you only do post reflow inspections for solder quality?
Consider that actual use first. Then find the best machine to serve your needs at the price you can afford.