I actually considered trying random, but then the Base cards you receive will be random as well. Whatever Prism(s) you're using when you earn cards determines what Prism they are from. I figure it'll be easier to focus on 1-2 Prisms to get a decent card selection for Constructed, then I can rotate around to other Prisms if I feel the need to mix things up.
Either way, good luck on starting Conquest runs! :D