Shepard has superior AP by a long shot, greater range, equal durability and roughly similar hax power. The XCOM Soldier, on the other hand has better area control, resistances (immunity or at least massive resistance to psionics, fear, heat and poison) and superior hax variety, and a roughly equal intelligance.
At twenty meters, the first thing the two would do would be dart for cover, neither willing to see what their opponent's weapons would do to them, as they reach out with psionic/biotic powers. Neither would dominate one another, but they would both break off, exchanging ranged fire. Due to the XCOM operative's somewhat strange aiming and dodging, neither side would hit each other for quite some time, but after one hit, it would be back to the mental back-and-forth.
This would repeat several times until the XCOM soldier would attempt to tear a Psionic Rift, or perhaps Shepard throwing a grenade. Either way, another few hits, and the XCOM soldier would be able to mentally latch on to some kind of weakness in Shepard, and disorient him, or flat out kill. Alternatively, Shepard would manage to get a few hits in and turn the XCOM soldier to paste.
I declare it inconclusive, both sides can kill each other too easily.
