A few thoughts on crosswind stability.
1. Front wheels cause more stability problems than rear wheels because they have a steering axis (your handlebars/head tube). When wind hits your front wheel it can cause the front wheel to turn, which can cause stability issues, and for lack of better terms, scare you. The depth of your front wheel, and the shape of your front wheel both contribute to the instability. In most cases, the deeper the wheel, the more unstable it becomes. With respect to wheel shape, wheels that produce a high amount of yaw torque (a fancy way of saying the wind causes your handlebars to turn) are also less stable. Some of the most modern wheel designs have taken not only aerodynamics into consideration, but also yaw torque. As an example, our design algorithm included yaw torque as a parameter. This is because we know stability is important, simply because a fast wheel that is nearly impossible to ride, will slow you down because you can't control it.

2. The depth ratio of your front wheel compared to your rear wheel matters when talking about stability. As your rear wheels gets deeper with respect to the front wheel, your center of pressure moves towards the rear end of the bike. To visualize this, imagine you were looking at a picture of yourself riding your bike from the side. If you had to find the center of the "area" you create, that would be your center of pressure. As you create more rear area with a deeper rear wheel, the center of that area moves backwards. As your center of pressure moves backwards, you reduce the force on your front wheel, and in turn increase stability.

I've never had an issue with back wheel in windy conditions. It is always the deep front wheel that gives me trouble. I would say definitely go with the disc.