An attempt to summarise the situation as it stands:
Aguero's 1st choice would be a champions league team preferably real madrid since he bought a new expensive house in madrid BUT Florentino Perez and Atletico have agreed that Real will not activate the release clause, however that is not to say that Mourinho will not get his way if he doesn't get Neymar. (see Valdano getting the sack). There is also a vague interest for Aguero from Chelsea and Man City but no concrete offers YET (according to press reports).
The only real interest shown in Aguero by a club has been by Juventus who agreed terms with the player's agent back in May (even before Aguero announced that he wanted to leave Atletico - see first meeting between Segui and Marotta in Torino) and made an offer to atletico which was revised but as yet has not been accepted. Tuesday's meeting will decide upon the final offer and whether or not Atletico will accept it (it seems that unless there are any massive changes, according to Bronzetti, they are inclined to accept the offer).
If before Tuesday's meeting ANY team were to activate the release clause, this would give Atletico no choice but to let Aguero agree terms with that club and maybe leave if he chooses.
It will be up to him and this is where Juve is at a disadvantage because unless we know what Aguero thinks personally, it is safe to assume that he would pick a champions league team over Juve if he had a choice unless he is a diehard juve fapper like many people here

(and he is reading and fapping for over posts as we type).
Thus the only advantage Juve hold at the moment is the fact that they made a very early offer (in May) and are the only ones in the race since no other club wants to spend 45million on aguero YET. This I have deduced from Marotta's words (Juve will only lose Aguero if an unbeatable offer is made by another club which Juve cannot match).
The meeting on Tuesday/Wednesday (according to italian press) should provide a clear indication of what the outcome will be but I still don't expect any transfer to become official before the end of Copa America. Remember that to officially join he has to go through the medical and actually physically sign the contract and unless Juve fly out to Argentina I doubt he will have time to visit Torino before the end of the Copa.
If this transfer goes through, Juve will have signed a world class striker, an answer to cavani, ibra and eto'o, a star, a game changer, a marketable player (sells tshirts and stadium tickets) and will have invested heavily in their future (he is only 23 - Marchisio/Giovinco/De Ceglie are all older!). Champions attract other champions. Remember that having Pirlo and Aguero will attract other big names.
Over and out