So you are asking wich one is the deadliest, not the most destrucrive.
Either way I'll just give you my opinion.
Bijuu Dama, the most destructive out of the two mentioned has two drawbacks that I'd like to point out.
1. It takes a couple seconds to charge and while doing so it alerts your opponent of your next move.
2. (You could say is only 1 drawback, sense its connected to the one mentioned already) It gives your opponent time to think of a counter or way to evade it, thus being easier to dodge.
Shinra Tensei, the fastest one out of the two. And invisible to sight, making it really hard to dodge.
In addition it can also be used to pull your opponents or just toss them around. But it also has its drawbacks.
1.I you are strong enough you can resist getting pulled or pushed around.
2.If you have a good enough defense its alot esier to tank a blast from it than a Bijuu Bomb.
With that said, it depends on the opponent you are facing.
Example.
Bijuu Bomb is a better option againts Kakuzu
But Shinra Tensei is a better option againts Minato
At the end of the day its personal preference, sense they both OHKO most of narutoverse