Tomato plants aren't all the same. It's not just the different shapes, colours and sizes of the fruit, it's also the way the plants behave, or in other words, their characteristics.
One of the most striking differences to me is in the way their leaves react to different conditions.
Some varieties curl their leaves if the sun is too strong for them, others do the same if it is too cold at night. Some just like to curl their leaves whatever the temperature because that is a characteristic of that variety!
The difficulty is, if you only grow one variety and the leaves start to curl, is it too hot in the day, too cold at night or are they just happy!
I find that I can learn a lot by comparing the behaviour of one variety with another. For example, the varieties with potato leaves seem to love the full sun whereas Black Cherry almost wilts under the same conditions. Obviously I've now put the Black Cherry plants in a position where they will get more shade.
Another point here is that Black Cherry grows more leaves than many other varieties and therefore needs more water in its system to support the extra leaf area ... no wonder why it doesn't like too much sun.
The down side of a leafy plant is that it will need more watering.