Just from the examples you have posted, I would say you're an alto. As for what key you sing "best" in, well, it really varies from song to song. You aren't going to sing EVERYTHING in the same key. For example, you wouldn't determine "I sing best in the key of B flat, therefore, I am going to transpose everything I do into B flat." If you are only singing "for fun" in a karaoke situation, knowing what your actual range and keys are really isn't necessary. Just find things you like to sing. Determine what things seem to sit well in your voice, and what feels right to you. Most karaoke systems have the capability to adjust keys, so, if something you want to sing seems too high or to low for you, don't be afraid to ask the KJ to take it up or down a few steps until you find what works for YOU.
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"I hold the key to an open door....will I ever be free...?"