It's long been presumed that going first in the Arena was a huge advantage. With such a tempo based meta where board presence trumps all, it absolutely makes sense that this would be the situation. But our friends at HSReplay have examined 280,000 matches in January 2017 to find out if this was truly the case.
In short, it gives you a tremendous edge against your opponent if you're going first, particularly if you have a 1-Cost minion to play.
Here's the graph HSReplay whipped up to show the effects:
It turns out that some 1-Cost cards have more of an effect than others as well. For example, Raven Idol doesn't do nearly as much for your win-rate as Living Roots which can give you a couple of 1/1 tokens.
They also found the underlying average win rates for each class, putting Warlock as the best available at a 60% win-rate across more than 50,000 games. The worst? Druid.
For more statistics and analysis, head on over to their blog post.