A press brake is a simple machine with a lot of accessories that can connect to it. There are a number of things that you should consider when you want to purchase a press brake.
Length
Tonnage
Throat
Gauge
Energy Consumption
Angle Controls
and so forth.
The maximum length of the piece that you are using and keep the length of the machine depending on that. The tonnage (bending capacity) depends on the type of material that you are using, so, make sure that you try to fix the tonnage with a tonnage calculator or some other tool.