First if all we are talking ultrons physical form the internet can't help him here let's pretend vision wiped him out of the web now anyways I think help buster would win because it is as strong as the hulk and now has a 'healing factor' (auto repair) to fix himself up In seconds and he is so amored ultron has nothing on him he would break his puny metal fingers on that armor and he fixed that bug with the whole tearing out of the suit thing
Since Ultron is not one physical thing he could potentially take over millions of robots and all of them would still be him. Assuming he couldn't do this he would still defeat Hulkbuster Iron man. Due to the fact that Ultron has artificial intelligence in him he can think, plot and scheme as well as being incredibly strong. Since he was in the internet temporarily it is unknown just how much information he obtained. It is very likely that he looked up secretes about Stark that he is unaware of. Con's statement claiming that Hulkbuster can heal himself is technically not true. He has a limited amount of body parts so eventually he would run out. Due to his huge size Hulk buster would be unable to move at the speed of Ultron therefore Ultron has a speed advantage. Ultron can keep evolving as it has stated in the Avengers: Age of Ultron whereas Hulk buster stays the same. Ultron does not have any relative or loved ones. Tony does. This allows Ultron to target vulnerable relatives and friends of Stark - including Pepper Potts (Tony's girlfriend). Tony relies on Jarvis and others. Ultron relies on his own brain which was created by Stark himself using artificial intelligence.
Tony also has many disadvantages himself - as a person. He's a never recovering alcoholic. he supported the registration act, arrested captain america, cloned Thor that led to the death of bill foster, and was too weak to prevent Norman Osborn from gaining control... and despite all of this he still argues with Steve now that Steve has his old job. Keep in mind that the majority of Iron Man's adventures, especially during his first few decades, have been about have been about protecting his company's assets, a company whose main business for several years was selling arms. He wasn't going on patrol and protecting regular guys, he was more worried about his ability to sell weapons to the government.