1. Atletico Madrid

Nemanja Matic moving to Atletico Madrid would essentially confirm his status as a second-string player, but also presents the best opportunity in terms of competing with the best teams for top honours. Atleti's current midfield options include the likes of Saul Niguez, Thomas Partey, Koke, Hector Herrera, and Marcos Llorente, and it is highly unlikely that Matic seals his spot in such a versatile midfield.
Stylistically, Matic's profile could be a valuable addition to Atletico Madrid. Because they like to sit deep, soak up the pressure and hit teams on the counter, the Manchester United man could be the figure they rely on to break up play and dominate aerial duels. Standing at 6'4", Simeone could utilise Matic's physicality to tighten up the defence and protect leads during the closing minutes of matches.
On the other hand, Partey has grown into his role as a deep-lying midfielder and ran the show in the middle on a number of occasions for Diego Simeone's side this season. Saul is one of the Argentine's crown jewels along with Koke, who form what is essentially the core of this midfield.

If Matic does decide to join Simeone's Atleti, it would be the clearest indication that Matic is willing to play a bit-part role in an athletic squad of players and would rather help facilitate younger players coming through the ranks. The last few years have also seen Atleti part ways with a number of experienced heads such as Diego Godin, Juanfran, Felipe Luis, Gabi and more. Matic's addition could help bring in some more experience to Simeone's squad, as could that of Edinson Cavani, who is reportedly set to join Los Rojiblancos on a 3-year-deal after his contract with Paris Saint-Germain expires.
Regardless of whether he will be a hit at the Wanda Metropolitano, make no mistake, Atletico Madrid will comfortably be the biggest project that Matic could land this late in his career especially given his rapid decline. Should this happen, he could be a stop-gap squad player in Atleti's quest for silverware for a reasonable transfer fee.