Now who in the hell am I to say

? I don't own either one of these and have not gotten to try them either. I have been researching and making phone calls for months. About a month back I asked and pondered this same question. Much like Pulltab. I am buying another couple of detectors and want big bang for my hard earned buck. From people I have called and talked to that own one or the other and also from what I have read:
Xterra- not chatty, decent to great depth, flexible hunter with the different freq coil changes(not all the coils are submersible). (kinda like that 3KHz coil option) super easy to set-up and use. Additional coils seem a little pricey to me. Haven't found anybody complain about one yet. Obviously a great detector for the price!
MXT Pro- excellent depth, guys that use em swear by em period. (much like the 705 guys) Tons of coils available for these units gives you tons of options. A little bit heavier but it's not noticeable because it's extremely well balanced. Built like a high quality tank (not saying there is anything wrong with the 705's build). It is an analog digital hybrid, has knobs over push buttons, some prefer this. Some say it can be a little chatty. To me chatty means good things because it means sensitive receiver with max depth. Some don't like that background noise. Super easy to set-up and use. Back lit display. Obviously a great detector for the price!
Orgin: One is the US, the other is overseas.
Then you can add a MXT, M6 F70, F5, Vaquero, Outlaw, Omega 8000 and many more to this list and research them to death trying to find every and anything wrong with them (I have!). What I have finally concluded is they are all great detectors some just seem to lend themselves better to peoples needs and methods of hunting. Depths on all these single freq. VLF detectors are pretty close with an inch or two of each other. The FCC limits max transmit power. All the receivers are capable of good/max gain. (At some point there is diminishing returns on excessive gain). So after the receiver we can do some digital filter or digital magic, but all in all they are pretty close in depth and probably have been for many years now.
So anyways, I pretty much have my mind made up on which one I am going to get,,,,,,, BUT on the day I purchase if I find a good/great deal on one the those others--- anything is possible!! The bottom line is I will learn the one I buy inside out and become and expert with it and someday you will be asking my opinion of it!
I don't think you would go wrong with either on of these. Just my opinion.