There were a few things that convinced me that Jesus is not Michael. Some of the reasons are as follows:
1. There is NO scripture that directly states that Jesus is or was Michael the Archangel.
2. The book of Hebrews chapter 1 was written for the purpose of denying that Christ is an Angel and clearly shows the opposite which is that Jesus as the Son of God is superior to any of the Angels.
3. In order to come up with such a strange teaching, the WT twists the scriptures to say things it does not. A prime example is with their interpretation of 1 Thessalonians 4: 16. From the NIV it states;
16 For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first.
The WT reasons from this verse, that Jesus is the Archangel because he is giving a loud command (or shout) WITH the voice of the archangel. However, this verse identifies Jesus right in the beginning of it as "Lord" not the Archangel. Also to reason that the Lord coming "with" the voice of the archangel means he IS the Archangel is incorrect. If it is true, than his coming "with" the trumpet of God would mean he IS the trumpet of God. "With" simply means accompanied by.
Hence, this verse is saying when the Lord comes down from heaven, his return will be accompanied by a Loud Shout from an Archangel and the trumpet of God. It is not saying he IS the Archangel.
Other Scriptures support this verse and the fact that Christ will return with the Angels (Archangels too)
"When the Son of Man comes in his glory, and all the angels with him, he will sit on his throne in heavenly glory
I wrote a paper a few years ago debunking scripturally the WT teaching that Jesus is Michael. If you or anyone else is interested in a copy please email me here; [email protected]