It's been a busy summer transfer period for Manchester United. Ed Woodward and Louis van Gaal have already brought in 4 players in Bastian Schweinsteiger, Memphis Depay, Morgan Schneiderlin, and Matteo Darmian.

This was exactly what United fans wanted, and has filled in many gaps, as well as bringing in top quality names; Schweinsteiger in particular. There is still some gaps, however; and the main position that springs to mind is a centre-back. 

Manchester United are always linked with a number of players, but this summer the two that have been constantly mentioned are Nicolas Otamendi and Sergio Ramos. The question is; Who should United sign next?

Ever since the departure of Rio Ferdinand, Nemanja Vidic, and Patrice Evra; United have lacked a leader at the back, and both Ramos and Otamendi have leadership in their locker. 

Should United sign Ramos?

If Ed Woodward was to splash the cash, Sergio Ramos would bring a number of attributes. He has a significant amount of experience, including winning the Champions League and World cup. 

Abilities 
Sergio has proven himself at the top stage for many years now, and has captained Spain and Real Madrid. With great ability in the air, United's set piece struggles across the 14/15 season could be over. Sergio Ramos has been in Spanish football for many years now, and knows how to keep possession, something Louis Van Gaal looks for in every player.

Spanish Connection
Who could forget? With Juan Mata, Ander Herrera, and David De Gea; Sergio Ramos will know plenty of bodies in the dressing room, which will help him to settle in and get to his devastating best early on. This also brings the possibility of a David De Gea contract, but that's another story.

Despite all these pro's, Ramos is 29, with Otamendi a bit younger; and available for cheaper, is he the better option?

Should United sign Nicolas Otamendi?

Nicolas Otamendi has had an outstanding season, and eased himself into the La Liga team of the season. Otamendi has lead from the back, and been the soul of everything Valencia have done over the course of 2014/15. 

Argentinian connection
The Argentinian connection. With Marcos Rojo enjoying his time at United, and Angel Di Maria still currently at United, Otamendi will find it fairly easy to settle in at Old Trafford.

Otamendi definitely wants the move, with the player reportedly not turing up to Valencia training, similar to the situation of Marcos Rojo last summer. If Louis Van Gaal does go for Otamendi, it also would seem likely that De Gea would be at Old Trafford for at least one more season.

Both players are obviously top drawer, but who will Louis Van Gaal pick up next? Only time will tell.