Your question is kind of like asking do you prefer a BMW or a Porsche? That's something that sound quality should decide, but IMO you can't go wrong with either unit.
However if it were my money, I'd go separates as others have suggested. An Aurender N200 and a Denafrips Terminator Plus 12th DAC can be had for similar cost as the A20 and X1....and that would be world class. I'd also throw the Weiss and T+A DAC 200 as options if one were so inclined.