Well a good guess would
US (F16 and F18 have been on the table for a while)
Russian (Standard options will be Mig29's or 35's maybe the Yak 130 but the last one is unlikely as it is subsonic and the requirement is for supersonic)
China (JF17)
French (Surplus Mirage 2000's )
Israel (KFIR was on the table before and may be again)
All of the above are sanction free. As I have repeatedly said the FAA prefer western aircraft so the US, Israeli and French options would be probably in the lead. It will boil down to money and more importantly politics.
Depends on the results of the elections too. The Pro-US party seems to be on the winning side. If they win. Highly unlikely JF sale occurs, they will go for F-16 if possible.
Though these birds are sanctioned free, argentina is in a position where it has more issues than just sanctions.
1. 26 F-16 Block 50 (with 2 P3C and 3 tankers and AIM120) is the deal US offered them. Here they have two issues, one is obviously the price, this is going to be extremely expensive, even if they go for the fighters. The second issue is the UK. The UK blocked the sale of trainer aircraft like FA-50 to them, they will throw a massive tantrum if their closest ally tries to sell Aircraft with these capabilities
and tankers allowing them to reach British isles and Maritime patrol aircraft to threaten their ships. Even if Argentina has no plan to do so.
2. Russian options are already off the cards imo. Argentina buys all of its other military tech from the US and it’s Allies (France), This would lead to major sanctions.
3. The JF-17 deal is under pressure from the US (and to some extent even the UK). And a lot of pressure internally in Argentina where one partys agenda is more Pro-China (or anti-west) and the other is the opposite. And the Pro-western party, so far, seems to be the favorite for the upcoming elections.
4 and 5 are the easier options, but they’re also used and less capable aircraft as they wouldn’t be getting the weapons packages they want with them. However if they wanted an easy way out, this is what they’d buy.
This is why I ask Pakistanis not to celebrate prematurely, the possibility of this deal has a very high chance of sinking, if it has not already, but we’ve already made a fool of ourselves by posting it everywhere and celebrating. Notice how all the media went absolutely silent after the Argentinian MoD denied the deal. (It’s still not that they didn’t want the JF-17, their Air Force totally did. But they have other factors pushing them away from it)