Power up a 98% background. Or a 3 star shiny no background?

Hey guys with all the Go Fest stuff coming to an end. I managed to get myself: a hundo mewtwo no background (maxxed already), a 98 background, and a 3 star shiny (no background 😔)

I have enough candy to max out one more mewtwo. Should I max out the 98 with the background? Or the 3 star shiny no background. Or should I just wait

I really love the background and wish my hundo had it but oh well, what do you guys think