We know Ultron created the android "Vision", and then imprinted Wonder Man's memory engrams on it, but eventually the Vision turns on Ultron and actually becomes an Avenger.
Has Vision ever shown himself to be stronger/more powerful than Ultron within the same canon universe?
No. The Vision, while eventually turning on his master Ultron-5, he was in no way a match for the malevolent machine if he fought alone. Ultron is possibly one of the most powerful foes the Avengers have ever faced.
. He may become partially or completely intangible, making him immune to harm, phase through walls or allowing him to partially solidify inside a target causing incredible pain or damage. This intangibility gives him a semblance of low speed flight as well.
. He may alter his density making him as tough as diamond and giving him superhuman durability while increasing his strength (enough to press 70 tons).
. He may channel energy absorbed through his body and redirect it with his solar jewel on his forehead. He is capable of generating force blasts or melting materials with it.
. He can be damaged and repaired assuming the technical expertise is available. He has experienced destruction several times and returned to active duty.
Unfortunately, NONE of these powers is enough to stop Ultron-5 whose durability was that of adamantium, and had no serious physical weaknesses at all.
Stronger than any single Avenger at that time except Thor and Hercules He was capable of pressing 100 tons easily.ron brings the pain with the force of Thor's hammer to Wonder Man and Thor simultaneously.
With his outer shell composed of adamantium, Ultron was proof against almost any form of damage and immune to the Vision's intangibility. He was easily able to resist blows from Mjolnir and Thor's magical lightning could not harm him.
. Superhuman Durability: Ultron's outer shell is usually composed of Adamantium, rendering it almost totally impervious to damage; however, his internal mechanisms are generally less durable and more easily damaged. His skin composition is about (.5 inches thick), neck, knee, ankle, elbow, shoulder, wrist, and finger joints are finely tessellated titanium alloy to permit flexing. He is able to withstand concussive blasts and heat of a 100 megaton atomic bomb.
. Ultron possessed a number of energy projection capabilities including powerful plasma energy blasts, radiation beams, tractor/pressor fields and his encepahlo-beam capable of rendering living targets into a coma-like state.
. True adamantium Ultron used to give the Avengers hell on a semi-regular basic. He would take on the entire team, Thor included, and only end up being defeated because of things like Wanda's hex affecting his molecular rearranger, or being trapped in adamantium. It was said that he didn't fear Thor, and Thor's lighting strikes and hammer blows had no real effect on him.
It would take the entire Avengers to defeat him once his body was upgraded to pure Adamantium. Unfortunately, the same hubris that leads Ultron to fight the Avengers is almost always his undoing in nearly every confrontation with them.
Assuming you're referring to Ultron-5 then the answer is an emphatic yes. Ultron may spend much of the time rebuilding himself, including upgrades at each turn (for example trying to upgrade his body to Adamantium, building an army of robots, etc) yet he is constantly thwarted by the Avengers on an almost clockwork basis.
Ultron-5 was able to control Vision through the use of a chip in his brain. Once that chip was negated, Vision was able to function freely as an individual and is certainly a match for Ultron given his extensive range of superpowers and Ultron's bizarre inability to stop himself from self-destructing (facepalm).
As baddies go, Ultron is the diet coke of evil and pretty much a punching bag for whichever superhero is having a momentary crisis of faith that week.