How to judge a 3D printer.

In this post I want to list the things that matter when you buy a 3D printer:

Creality CR10

Point	Details
Bed size	While many crave a huge print-bed, I have found that most things I print are small. Why? Because most 3D printers are much slower than you think. In fact most points on this list are about speed vs. quality. But if you have a fast printer that prints high quality, or if you really need to print big and have the required patience, then bed-size is still important.
Motor speed	How fast can the motors transport the extruder around the work?
Motor torque	How fast and steady can the motors accelerate?
Extruder max temperature	Will the extrude cope with the high-temperature filaments?
Extruder temperature stability	Will the extruder manage to hold temperature steadily during printing, even at higher temperatures?
Extruder temperature speed	How fast will the extruder warm up from room temperature at the start of the print?
Bed max temperature	Will the bed cope with the high-temperature filaments?
Bed temperature stability	Will the bed manage to hold temperature steadily during printing?
Bed temperature speed	How fast will the bed warm up from room temperature at the start of the print?
Enclsure temperature control	Some filaments like ABS may require the temperature around the work being managed using an enclosure and heater.
Direct vs. Bowden filament feed	The size of the print head directly affects the speed and accuracy of your printer. A big head will slow down and cause the printer to wobble if it is not rigid enough. To get around this many printer manufacturers look for ways to decrease the size of the head. One feature, the "bowden tube" allows the extruder motor to sit on the frame instead of the head. However this reduces the filament capacity somewhat which in turn affects print speed.
Interchangeable extruder head	You might only care about the standard 1.75 mm filament through 0.4 mm nozzle size. However there are lots of options out there when it comes to nozzle sizes. Having an easily interchangeable head/nozzle is desirable, and a printer that can handle the higher heat requirements of a larger nozzle/filament of course.
Multiple extruder head	Having more than one extruder provides some benefits, for example if you are printing with more than one material per part. Example usages are: flexible filament for rubber seals, washable support material, dual color prints etc.
Noise	Remember your printer will be running for a long time. Print times are usually measured in hours, and sometimes in days..
Build quality & basic features	This qill require a lot of "getting to know" the printer. Basically all sorts of small practical details such as positioning of the user interface, display size, where is filament dispensed from, how are the wires connected? etc. etc. You can often get an impression of these things by looking at printer reviews on YouTube.