This is about the hundredth thread of this type from the past two weeks, why not try finding another and just reading it or posting on it? However, now that you have started this one...
Modric is the only one of those players I would want, full stop. Eriksen, Gaitan and Gotze aren't naturally suited to the positions we need to strengthen, all three are more forwards than true midfielders.
Martinez, Eriksen and Gaitan are also not good enough. We have plenty of good players, what we need (if we are going to buy) is a world-beater who would walk straight into our first team. Only a real grass-is-greener thinker would think those three could do anything other than add to the numbers crowding the bench for most games.
Sneijder is well past his best, increasingly suffers from injuries, and badly off form at the moment. On top of that, he would cost a huge amount in both wages and transfer fees.
Hamsik is undoubtedly talented. Whether he is talented enough is up for debate, but for me the real problem is his attitude. He doesn't take enough defensive responsibility, and time and time again I've seen him drop out of games, looking increasingly frustrated, when things don't instantly go his way. One of the reasons we are successful at United is that Fergie thinks about much more than ability when he buys a player - he is careful to select players with the right personality and mentality to fit in with this club and its ethos, and to succeed. I don't see Hamsik being one of those players.
However, I would be happy to see us spend a large sum on Modric. He is exactly what we're looking for, and amongst the top six or so players in the world in his position.