Many years ago the WCG published a booklet with the title "Which Day is the Christian Sabbath?"
Wrong question. Why? It just assumes there is such a thing as a Christian Sabbath, and once you've conceded that it's all downhill; off into the proof texts. When it comes to a Saturday/Sunday shootout, based on duelling with Bible texts alone, the Sabbatarians can make a very good case.
The problem is that there's a degree of dishonesty in this approach. One false trail is to assume that there is such a thing as a Christian Sabbath. Another is to imply that Christians who attend services on Sunday are doing so under the illusion that they're keeping the Sabbath command.
The idea that Sunday was the Christian Sabbath first occurred in 17th century England under the baneful influence of Calvinism and Presbyterianism. This was the genesis of Sunday Sabbatarianism and advocacy groups like the Lord's Day Observance Society. The early Adventists were seeded with these same Reformed assumptions. Most non-Calvinist churches teach that there is no divinely appointed day of rest required of Christians. It hasn't helped that Christians have occasionally referred to Sunday as their Sabbath either. This was simply appropriating a biblical term, not adopting a commandment which they regarded as abrogated.
Why Sunday then? Tradition and convenience. If pressed, they'll talk about a Sunday resurrection, but that's not a command, it's a precedent and a sanction. There's no concept in their theology of an obligatory pre-set twenty-four hour period of sacred time. Christians, under this view, sanctify time by worship, regardless of the day. Time isn't "pre-sanctified". It's an important distinction and one that most Saturday Sabbatarians seem totally unaware of.
It's also why most Christians, other than blue-stocking Presbyterians of the old school, have no qualms of conscience about visiting the mall on Sunday afternoon or going to a cafe or watching the big game. The hour of worship is special, but not the whole twenty-four hour period.
So it's appropriate to reframe the question. Is there a Christian Sabbath? A Jewish Sabbath, yes. A Saturday tradition in parts of the early church? Yes. Beyond that, if you want to argue for a Christian Sabbath - whether Saturday or Sunday - you have to do a lot better than leaping straight in with the 'Which Day?' proof texts.