I am going to be vendor-neutral here and give you some information you can use to evaluate systems from a general perspective. Because I represent a specific manufacturer, and I don't used an enrober in a production environment, I am not going to offer my opinions of whether a particular belt is "better" than another. My impression, from watching people work, is experienced belt operators can accommodate to the specifics of any belt pretty quickly.
There are some things that would be really helpful to know when trying to answer this question for you. Chief among them is how many (per hour or day) of what kinds of things do you want to enrobe?
One thing to consider is that the bowl size of the continuous temperer is not the determining factor of throughput. If you want to enrobe (say) 250 pieces per hour and each piece requires 10gr of chocolate, then you only need 2.5kg of chocolate per hour. You don't need a machine with a 25kg capacity working bowl that can temper 75+ kilos of chocolate per hour because you are never going to get close to needing (or being able to use) that much chocolate.
Belt width does affect throughput, but only to a certain extent. Very quickly how the work needs to be decorated becomes a more important factor to consider - and that will determine the number of people need to work the belt. For example, if you're doing 35x35x7mm piece and putting individual transfers on each one, you can get -- theoretical maximum -- 4 pieces per row and 20 rows per meter and if the belt is running at 2 meters per minute then you could (theoretically) be enrobing about 1000 pieces per hour. To reach that production you probably need three people working the belt. One person putting pieces on, another person taking pieces off, and a third person decorating the pieces. You'd be consuming about 10kg per hour of chocolate, so a machine with a 7-12kg working bowl capacity (20-45kg per hour of tempered chocolate) is going to be just fine.
If you are going to be having more than one person working the enrober, then the overall size and arrangment of the enrober belt and temperer need to be considered. It's probably better to have something that is larger in footprint than the smallest machine that will meet your needs.
In reality, there's no significant difference between the throughput of a 180mm belt and a 250mm belt unless the size of the pieces you are making demand that you do wider. Also, most cooling tunnels (should you need one) are sized for belts that are 300mm and wider. As I hinted at above, once you get past a certain throughput, getting product on and off the belt becomes more and more of a challenge. Again, if you have a 300mm wide belt then you can roughly double the throughput of the 180mm belt: at 8 pieces per row, 20 rows per meter, and 2 meters per minute belt speed it means that the person (or people) loading the belt are putting down 320 pieces per minute. It takes skilled and dedicated people to work at this pace and the work itself needs to be extremely well organized.
Other things to look for:
If the pre-bottomer is a standard part of the enrober belt, not an option.
If there is a fan built in to blow off excess chocolate.
If there is a net beater to help remove excess chocolate.
If there is a de-tailer to remove chocolate that would form a foot.
If the chocolate veil is "double curtain" which means that there are two streams.
If the height of the curtain veil is adjustable.
If the speed of the belt is fixed or adjustable as a standard feature
clay - http://www.thechocolatelife.com/clay/