united fans overrate CR7's time in united. rooney was clearly better than him in their first 3 seasons together and played a very important role along with tevez in CR7's 42 goal haul in 07/08. people make the mistake of taking CR7's goal exploits at madrid and extrapolating them back to his united years. he only scored 119 goals for them over the span of 6 years. that's comparable to neymar's haul at barca over 4 years and neymar definitely isn't a barca legend.
Rooney was only really better than Ronaldo in his debut season (2004/05) but that was more due the fact that he was at a more advanced stage of his development than CR who was still very erratic and inconsistent with his decision making and end product. He often held onto the ball too long and over-dribbled (often beating a man but then going back and trying to beat him again). He'd try to pull of the most outrageous tricks in games much to the frustration of Van Nistelrooy at the time. However, once he began mending those weaknesses in his game, he completely eclipsed Rooney. Think it was the second half of the 05/06 season he really took off and became a key member of the United team at the time. By the time the 06/07 season came round (after the '06 WC) he was a different beast and was the primary catalyst to united winning the EPL that season which resulted in him swooping all the major individual awards in England that year ahead of guys like peak drogba, peak gerrard, lampard etc. before finishing 2nd in the Ballon D'or by the end of 2007.
Then came the 07/08 season when he scored the 42 goals and won the EPL + CL with United that saw him crowned as World's best. Don't think Rooney could even clean his boots that season although he was important for United too. But it was Ronaldo who carried them for most of that season at a time he was more than just a glorified goal scored. He was pretty central to everything they did attacking. His level dropped however in the 08/09 season (his final season at the club) but he already had his mind set on Madrid as he was convinced by Alex ferguson to stay an extra year when he was really supposed to leave in 2008. Is say their level was closest this season but Ronaldo was still better and together they won the EPL for a 3rd straight time and made the CL final.
Overall for their time together:
04/05: Rooney > Ronaldo
05/06: Rooney > Ronaldo up until about February 2006.
06/07 Ronaldo >> Rooney
07/08: Ronaldo >>>> Rooney
08/09: Ronaldo > Rooney (closer than previous two seasons) but it was mainly Uniteds defence of Rio/Vidic that carried the team to the title.
Overall, at their best for United Ronaldo was probably miles ahead in terms of ability and peak performance and Rooney knew this so didn't complain when he was being shifted around by Sir Alex towards the end of their time together to accommodate for the Portuguese.