For the first time this year, shifting transmissions from a variety of suppliers and in a variety of configurations are available to teams off the shelf. As such, I suspect a disproportionately high number of teams will be employing 2-speed drivetrains.
I'll also give my vote to the WCP gearboxes. 1515 is using the
2-speed WCD model this year. In all likelihood, we'll stick to the stock ratios (30-45, 15-60). This leads to fairly optimized speeds with 4" wheels. With that said, as Michael mentioned, changing ratios in a shifting transmission is as easy as finding 2 gears that add up to the same tooth count.
I suppose your choice of gearbox will, in the end, reflect the way in which you use it. If you are direct driving, and building out of 2x1 tubing, the WCP option is proven by a number of powerhouse teams. WCP uses hobbed and coated and Type III anodized 7075 gears that 1323 and other teams have been using in the past few years. While I haven't tested them yet, they are purported to be of great quality. The Vex ball-shifters are equally applicable, but can also be more easily used in dead-axle and non-direct drive applications. As an alternative, the
AndyMark product line has seen many seasons of wear and is probably your safest bet.