These are good machines within their limited range of travel. As with any machine you will need to learn a lot about set up and adjustment. I have assembled and adjusted both an X1 and an X2 and I don't find any real difference in quality. The X2 has a tilting column and I wish it didn't. That tilt mechanism is a major factor in the column flex that dogs the X2. I never tilt it, I see no reason to tilt it and a lot of effort has gone into reducing the flex and eliminating the need to re-tram. The rigid column of the X1 required some shims to get it trammed but after that it was not a problem. The X-Y table design and adjustment are virtually the same and rigidity is equal but the X-1 has less travel. The Y axis travel is very different. On the X1, large movement is made with a lead screw and is slower than the Rack and Pinion of the X2 but is much more precise and I never had the head creep down on the X1. The X1 has a quill mounted spindle which is used for fine adjustment and for drilling. It is a much better drilling machine than the X2 which requires you to muve the head up and down the dovetail column with rack and pinion. You must maintain the gib adjustment carefully on the X2 to get smooth travel. On the other hand the quill travel on the X1 is very small (about 1"). You can still move the head up and down with the lead screw to achieve greater hole depth. The biggest drawback with the X1 is the same as with all small mills, you will have a hard time finding a really good vise that will fit. I relied more on clamping to the table with the X1 which increased set up time greatly.
I have never owned or used a Shereline or Taig machine but owners do amazingly precise work with them but there has also been a lot of fine work accomplished on the Unimat S-100 and its cousins. Whatever you have, you will learn to make it work.
Jerry