My personal opinion on the matter is:
Our original policy, before Ronaldogate, was to sign a striker with experience, as stated by Fergus. Berbatov is clearly the front-runner, i have to say that apart from a quick chase and rebuff by Lyon (for Benzema), he has always been the striker most likely to be signing this summer.
Now, i don't know how substantiated these reports are, but Ronaldo has burnt his bridges - there is very little way of him returning to the club after such a blatant disregard for his contractual agreements, Fergie won't have a player compromising the club in this way. Some might say that Fergie has never sold a player that he didn't want to sell, you are correct, but when was the last time he let a player get bigger than the club?
He has never, and will never.
At the end of the day, if Ronaldo leaves, we can directly replace him with a winger. The only problem is that there aren't any wingers in the same talent bracket as him, well, apart from Ribery, who would be bound to cost in excess of £40 million - hmmm. However, Aguero has comparable talent/potential as that feckcunt Ronaldo, and even though he prefers to play in a similar position to Tevez and Rooney, i think that he could more than effectively play on the same pitch with both of them.
He isn't an out-and-out winger, nor was Ronaldo last season, but he has the speed and skill to beat men and put defences on the back foot. Couple this with Rooney, Tevez and very possibly Berbatov and you have a hard-working, skillful attacking unit that has the variation of talents to absolutely rip teams apart. Ronaldo was fantastic last season, brilliant, but he scored goals, and goals, he didn't provide in the way he did the season before. Those goals can easily be replaced, Tevez and Rooney have more in them, our new striker (Berbatov) will, and if Aguero were to come i would expect that he will.