I have owned both the Makerbot Replicator 2 and the Ultimaker 2. I purchased one of the early MB Rep2's and sold it after 2 months of frustration. It did not have the upgraded parts that MB provided later after I sold it.
I did my homework after the first purchase disappointment with the MB. The conclusion I came to was that the Ultimaker 2 was the one to get. I purchased it from MakerShed and saved on the shipping costs that Ultimaker charges. The new UM2 was very nicely finished. It seemed more refined than the MB2. I carefully set it up and to my happy surprise I started printing successfully right from the start. Then after a few days the problems started happening. Clog after clog after clog. I searched the web for answers but found few as I had one of the first machines in the US. At first Ultimaker was responsive and tried to solve my problems. After many hours of searching for the problem, I FINALLY discovered what was causing all my grief. I contacted Ultimaker many times to let them know of the problem with the filament feeder design but thats when they totally stopped communicating with me. The knurled sleeve that attaches to the filament stepper motor kept slipping. It is held on to the round shaft of the stepper motor with a tiny tiny set screw (poor design IMHO). Once this tiny set screw loosens the filament can no longer be fed properly. OK you would think it's an easy fix...just tighten the tiny set screw. MUCH EASIER said than done!!!!! Access to the tiny set screw is totally blocked unless the stepper motor is removed. This requires dismantling parts of the printer. This takes about 2 hours to do. Then the problem is that the set screw is so tiny it's not possible to get it real tight so it will, as it did on my printer, come loose again. After fixing this 4 times I finally gave up on the Ultimaker 2 and returned it to MakerShed. I wish the factory would have admitted the design weakness and come up with a solution because the quality of prints it is capable of making is outstanding. Hopefully Ultimaker has corrected this design flaw...if they have then it is a fantastic printer but if they have not then I would look at other brands.
FYI...MakerShed was absolutely great to deal with. I would give them an A+++ for outstanding customer service.