I don't have any experience with these personally but the
Lulzbot Taz 6 and
Ultimaker 2+ both seem like really well designed, ready-to-go printers in your price range.
First layer adhesion is IMO the key to ease of use. if your bed is not perfectly flat or you have the leveling set incorrectly then you're going to have print problems, and resolving that ca be a pain in the ass. The Lulzbot line has automatic bed leveling, where it checks the distance of several points and then works out in software how to print "level" based on any deviation in the bed geometry. the Ultimaker uses a glass bed which makes for a perfectly flat surface to begin with (though it still needs manual leveling).
This is part of what makes the Prusa i3 such a great machine at a cheap price point, it has auto bed leveling with software compensation, and one of the few printers at that price range that does.
Second to that is just the general robustness and serviceability of the nozzle design. if the nozzle gets clogged or filament gets jammed how difficult is it to swap out. From what I understand both the lulzbot and ultimaker have easy to service nozzle designs.
On my own printer I have no automatic bed leveling and I've got an aluminum bed, the bed tends to warp over time which makes it a real pain to print (since once it's warped it's impossible to adjust to level). I'm in the process of building a glass bed for it. The nozzle design on mine is pretty great in that it's never clogged on me, however more than once I accidentally let it get to the end of the spool and had to disassemble the thing to swap the filament out (since there was no "tail" left for me to pull it out with). I'm not certain but I believe both the lulzbot and ulimaker have things in place to protect against this.
The ultimaker uses a "bowden" extruder which means the motor that pushes the filament is mounted outside of the build area and it pushes the filament down a tube toward the hot end.
The Taz6 uses a normal style extruder, which has the motor mounted directly above the hot end and "pulls" the filament in.
I'm personally not a big fan of the bowden style extruders as any flex in the material means that the extrusion is going to be less accurate, for instance they really can't do "ninja flex" or other similar materials because of this (it tends to bunch up and clog in the tube, or fail to retract properly). But they do have the benefit of much easier serviceability and much less weight on the gantry which means the gantry servo motors are less stressed and will likely be more accurate.
