It would be preferable only if focus is avoiding pain.
However, Jesus wasn't focused on avoiding pain. He was focused on opening the gates of Heaven, and the only way to do that was to offer Himself as sacrifice. His acceptance of the Cross is akin to jumping in front of a bullet to save humanity from certain death. Sure the bullet hurt - a LOT - but His sacrifice meant humanity could one day reunite with Him in Heaven.
A lot of people forget that Heaven's doors were closed to us after Adam and Eve chose to remove themselves from God through sin. Because of that choice, Heaven was no longer our birthright; instead of inheriting Heaven, we inherited sin.
Jesus, by living completely united to God the Father, restored to us our birthright through accepting even death on a Cross. He suffered the torment that is due each of us so that we would not have to. If we, too, choose to offer ourselves in union with Christ, God accepts even our tiniest acts of love as gifts and welcomes us back into His Family.
Suicide would have robbed Him of His ability to endure this full measure of sacrifice. Each pinch of a thorn, each crack of the whip, each stubbed toe along the Via Dolorosa acted as one more act of reparation to appease Divine Justice. And it was through even the wound to His side that His Precious Blood flowed forth, effectively anointing us as His children.
Remember, blood is the very essence of life. Jesus gave to us His Life, unto His very last drop of Blood. His Life is eternal, and thus we are able to take part in eternity with Him.
Suicide shows a lack of trust in God's Plan for us. It stops God from being able to help us grow and love deeper.
God the Father needed Jesus to walk this difficult road because someone had to show humanity how to suffer for love of others. Jesus perfectly showed how much we should love one another: Give completely of ourselves despite pain, humiliation, derision, and even death.
As St. John of the Cross has said, "[Love] is the bearing of another's burdens."
Jesus, in the perfect way, bore the burden of sin. And God the Father, in effect, sacrificed His own Son so that we may one day be joined in Heaven.
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