I agree that you need to try them out. I spent several years going to quilt shows with my own materials and trying out every available sit down. I discovered that I liked just about all of them, but had some favorites. Because we are on a fixed income I needed to find a good condition used machine and armed with my list of favorites I spent another year watching ebay, facebook marketplace and googling used long arms.
I was able to find a barely used Sweet Sixteen with everything I could possibly want on it at a price that fit my budget.
I’ve had it for a year and a half and have no regrets, thanks to having spent lots of time looking.
Of the ones you are looking at: I’m pretty sure that The Viking Platinum16 is made by HQ for Viking and is the same as the Sweet Sixteen. What I liked about the SweetSixteen was: HQ’s great reputation for customer service and the availability of couching feet etc.
The Juki was also one of my favorites due to visibility around the needle and some neat features like having a handwheel in easy reach from the front of the machine which is something that none of the other machines has as far as I know. That feature makes it very easy to position you needle exactly where you want it when starting to stitch.
As you test out different machines you’ll start to get a feel for what features you want.
Rob