Please level Prides. Prides are GOOD. The only time when a Pride isn't as good as Assault is during Burst Hour, but you're not going to need the help during Burst Hour anyway.
Ultimately, you take what you get. If you have SSR Prides, you use SSR Prides. It only becomes a question once you have a full, MLB SSR Grid, and at that point... you take whatever FLB you get. And it'll probably be Prides thanks to Union Events.