Here is a man who makes more first impressions than most, and sometimes to the same people. But for me his entrance from the first episode of the BBC reboot, the episode "Rose".
The set up was classic, of course it helps that the audience mostly knew what the doctor is, but it's fascinating that his introduction to Rosé is not some exposition about his time machine etc. instead he is busy bombing a building to deal with a bunch of autons. best damn quote, "I'm the doctor by the way, and you are?" "uhm Rose" "pleased to meet you,now RUN FOR YOUR LIFE!"
It's an impression that has brought us 7 more seasons of the galifreyan with the England obsession's adventures, so I guess it had to be pretty effective on us too.