The two models are different enough that you're not really comparing competitive models.
I like external knobs for manual adjustment, which is a nod in favor of the MXT. However, I do NOT like to have one control that ties the Gain (pre-amp gain), Modulation (audio saturation), and Target Volume all into a single adjustment function. That's one of the reasons the MXT fell out of favor with me.
There are a number of excellent coils for the MXT/DFX models, and the XLT has an ample number of good coils for it.
With regard to "programs", the XLT is the one that is 'programmable,' and not the MXT. The MXT is a very versatile model, and there are many ho prefer it's slow-sweep, quick-response performance, especially when hunting for the lower-conductive targets. Of the two, the MXT is most definitely the better unit for electronic prospecting, but the XLT has a solid following ... and for very good reason.
A person really has to analyze what type(s) of applications they will use a particular make or model for, and the coils to best handle the tasks. Since there is no 'perfect' all-purpose detector, any serious detectorist will have at least 2 or 3 on hand to best handle the needs that arise. Certainly, one of either model will satisfy a lot of people. Just pick the one that YOU feel most comfortable with and confident in.
Monte