Aggression and jumping when meeting people on walks

[gudrunit]

My 3 yr old male boxer always jumps on people and shows aggresson towards me and the people I meet when we are on walks. This only happens when I stop to talk, which is almost impossible since he takes all my attention.
He is very good on leash otherwise. I've tried some different things but with no improvements. This is worst when I use the Easy Walk shoulder harness, so I'm inclined to start using the Head Collar only.
I've been training him a lot since I got him (14 months old), had a lot of trainers help me, taken a class with very fine results. It seems that he wants to have all my attention when on walks, but he gets very easily aroused when guests visit also. But in these instances, old problems arise (biting on the leash, jumping up on people, barking and showing aggression).

Help me please