You'll have to consider for yourself what your own thoughts are, but some of the issues were these:
The United States saw the use of the atomic bombs as a way to bring the war to an end in a way that would cost less American lives. A land invasion of Japan would have meant many American soldiers being killed in battle. However, the cost in Japanese lives was enormous by the use of the bombs, and that was not given equal consideration.
Another consideration was that the United States had been engaging in a fire-bombing campaign of Japanese cities prior to the use of atomic bombs. The fire-bombing campaigns were horrifically destructive also, but did not have the radiation after-effects of atomic bombings.
An option that could have been used rather than dropping atomic bombs was to enlist Soviet troops in a joint invasion of Japan. But the USA wanted to avoid postwar Soviet presence in Japan, and the atomic bombs were seen as a way of ending the war quickly. You can consider whether it would have been a more "moral" way of pursuing war to conduct a land invasion with Soviet assistance.
Finally, the escalation to the point of using atomic bombs was, in part, due to the Allies' insistence on an "unconditional surrender" by Japan. A second bomb was dropped at Nagasaki after the first was dropped on Hiroshima, because Japan did not submit to unconditional surrender in the immediate aftermath of the Hiroshima bombing. You can consider for yourself whether some other resolution besides "unconditional surrender" was a viable option for ending the war with Japan.
