I'm not sure I follow your drift mate.
Eriksen's won more than Modric over the past few years? Back to back Eresdivisie titles and in this Season in particular he had a big impact, probably the biggest in the team alongside Vertonghen.
If you mean 'Premiership-proven' then of course Modric's got the upperhand but I'm not sure it's a no-brainer at all as Eriksen has got the potential to be better than Modric within few years. And as one is 6 years older than the other I know where I'd put my money at least.
According to wiki Modric's already a United-player?
The point rurik is making is highlighted by your comment above.
If the mancs are looking to win the title next season (which is what they most definitely are) then Modric is the obvious choice. He's a proven performer in the league they want to win. Eriksen may well prove to be a better player in 3 years time but that's an utter irrelevancy to the title next year.