Southpaw right hook. Although I've been working a lot on uppercuts lately and they're climbing the charts.
What punch isn't important, the best part is the trail of flying sweat (or even blood perhaps) when you twist someone's head :yep Woooosh.
I used that on my mate in sparring, his ear was purple for a week. Must've been a weak spot in the headgear
Anything thrown from my right hand as a southpaw. I'm right handed but my left needs improving, i've got a pretty good straight and uppercut(only when on the inside), I need to improve the technique in the left hook.
God I'll never forget the first time I did that...I've still got a perfect mental picture of the blood flying out of his mouth and my coach stopping in mid-instruction and going "Ooh..." ...And then I got beaten up. MY favorite punch...I'd have to go ahead and say whatever gets results. For me, a left uppercut to the liver or solar plexus (not a hook) can be really effective. Enough to freeze them, but not enough to put them down. Can land a TON of unanswered punches after landing one of these. It's nice because they get used to blocking your left hook downstairs, but that slight angle adjustment lets the uppercut land. Head shots, my most useful one is a chopping little overhand above the ear (or to the back of the head sometimes). I'm usually taller than my opponents and I like to go into a Philly shell on the inside or when I have them on the ropes. We usually end up left shoulder to left shoulder, and I'll either bump them and throw it or swing my left leg back while I throw it (to make space). I didn't think much of it until I noticed it's really easy to land and it tends to make people dizzy/open for more punches.
That is my strongest punch, after 2 rounds most people are usually pretty weary of it and leave openings for me to land right hands to the hand. My favorite punch to land is the right uppercut, I just love the feeling of timing it right and having it land home.