I really don't like the modern BT ones. While they are clever in design, they stick out too far from the wall (and the MK3 specifically being square, makes it look like it sticks out more than it really does) and I had issues with the line dropping because the RJ11 cable was not making good contact due to it being a combi RJ45 socket in the MK3.
In comparison the original ADSL v1.0 I have on my main line has been very reliable. I'd replace the MK3 with one, if I could find one.