Which 3D printer is good for beginners?
Which printer for a beginner depends far more on the beginner in question than the various printers available. 


If you are comfortable assembling parts and figuring things out a number of options exist. 
If you need a fully-built object, a number of options exist.
If you require lots of dedicated support, via phone or email, there
are options.
If you can ask questions in a forum and get the answers you need (or
figure things out when you don't and post your answers for others to
find) there are options.


If you have special/esoteric printing needs, that puts constraints on - if you kinda vaguely want a 3-D plastic printer, but don't really know what you want to use it for the field is wide open.