Lets put the positives of each team and weight it ourselves :
Barcelona :
-Compete for Prizes straight away
-Have competition so not first team straight away but will challenge and grow better
-Same school of football as Ajax
-Messi
-A team mate, Nigel De Jong just signed
-Lots of Dutch legends from Barcelona
-Better Football
-Has mentioned interest in Barcelona
United :
-Better Salary
-Will be first team straight away
-Can be part of a new building project
-Team CEO Van Der Sar and Blind from United
-Riola prefers money and in good terms with United
-Language
-Might be captain soon as United missing a leader
Thats all I can think of at the moment feel free to add anything more.
The way i see it is:
Raiola is pushing towards United because we will pay the demands and if De Ligt goes to Barcelona now he will be there a long time or his whole career. Why have a client make one move when you can have him possibly make two or three moves? Each of them with a payout for Raiola. He will sell it to De Ligt as United is a step up from Ajax (You may argue this due to champions league but the EPL and United are both alot bigger in stature than dutch football especially when Ajax will lose players this transfer window). He will tell De Ligt that if things aren't going well within 2-3 years, we can make some fuss and get a move to Spain or Italy. Meanwhile, United will be using 'the project', No 5, Captaincy, Money, ex-players..everything in their power to try and sell it to De Ligt. On top of this, Im sure i read a while ago that De Ligt is a massive fan of the EPL and had been told by many Dutch legends that a move there would serve him better right now, learning in a competitive and physical league at a young age, l don't know if i am imagining that or not but either way, the EPL is proberly serving is a draw aswell. All in all, i believe that a move to United is just as likely as a move to Barcelona. Especially, when Barcelona seem to have a lack of funds to do everything they want to do in the market in this window.
Anyone thinking the Copa Del Rey will have any effect are being stupid. IF Barcelona couldn't match the demands before that game, Do you believe they will break their wage structure and give De Ligt what he wants because of one domestic cup final when they are league champions?. If anything, they will tie up the Griezeman deal or a similar attacking transfer. Barcelona will answer losses with attackers, not defenders. If they have the financial ability to meet the demands.
Could go either way but i think its 50-50 and people thinking he wouldn't pick United vould be suprised.