Personally, I would not consider the Rostock for a beginner (note, I am speaking from experience using the v1, so I could be wrong about the latest v3, take this advice with a grain of salt). When I had picked up my v1, it kept jamming and the movement of the arms were showing slop (kept sticking or overshooting, depending on very slight adjustments to its tightness), it wasn't until I bought a few upgrades from Trick Laser (brand new arms) and got a new hotend (E3D v6 I think) that things started to go smoothly. That being said, I've been a 3D printer hobbyist for a while now, and I still have trouble printing large objects due to warping and splitting, so having such a large build volume doesn't necessarily mean better. I will say it's not so pleasing having to cancel a 15 hour print when you're about 5 hours into it.

As for the LulzBot, never had it, but it looks like a pretty standard Cartesian model. For the price, though, it seems a bit expensive for what it gives you out of the box.

If I were to recommend anything, I would probably suggest the Flashforge Creator Pro. It has a smaller build area, but for the price (less than $1000) and what you get directly out of the box (Dual extruders, heated platform, enclosed build area, LCD + SD card reader, two random 1kg rolls of filament, etc) it is totally a steal. Most of the features it comes with would have costed you extra making those upgrades anyway. Even though it is pretty cheap, they did not sacrifice part quality; I have had no urge to upgrade anything except the spool holder arms (since they only fit Flashforge brand spools), luckily the arms detach and replacements can be 3D printed.

- Lochemage