In my opinion, the depth is about the same on each one. Seems to me that they only added a lot of adjustable "bells and whistles" when the XLT came out. Others would argue: "yes, more bells and whistles, but you can use those bells and whistles to get more depth".
But depth debate aside, I preferred the Eagle over the XLT for other reasons: The XLT has an annoying delay in the display. Ie.: there's a moment from when you pass over the target, to when the TID comes on the screen. But the Eagle was instananeous. Numbers flickered right as you were swinging on the target, making the response much more likable. Also the Eagle (at least mine did) had the interesting quirk of being able to click the toggle while in disc. mode, when you were kind of over a target. It would de-tune to whatever you'd clicked near, making for a cool sort of pinpoint trick. Of course, you had to make sure that when you clicked the re-tune, that you held your coil in the air, away from all metals. But that became second nature to Eagle users. The XLT on the other hand, would re-bound to full disc. strength no matter where you clicked it. Jimmy Sierra told me that the initial prototypes of the Spectrum (the XLT forerunner) didn't have that capability. So he told the designers to make it so it re-bounded to full strength, instead of de-tuning to whatever you clicked near. His logic was that some beginners may ignorantly click near a garbage can or something, and not realize they were now de-tuned. Bummer that they decided to do that, because I found the de-tune feature to be quite helpful, when used right. It was almost like clicking to a smaller coil with the click of a switch, and then click back to full strength by clicking in the air.