Way back when I took accordion lessons, the big question was how many bass “buttons” you wanted; more buttons, more expensive. I started out with as “12-bass” (12 buttons), which is all you’ll need for a while. The standard is 120 buttons, but I’ve seen 150 also. How many shifts you have also determine price. A beginner’s accordion generally has 2 (violin and bandoneon were the ones I had). The next is the size of the keyboard; that is, the number of keys.
Now as far as which are the best accordions? I have no idea. Hopefully someone who has more experience than a couple of years of lessons when they were a kid will come along.