Berbatov scored nearly 50 PL goals for Utd in +/-100 appearances, won the Golden Boot and had a massive contribution with his goals fto their title 2 seasons ago (around 17-18 points, iirc).
Ultimately he didn't fit their system (flimflam) but his contribution was more than meaningful, imv
But besides that - I think Modric would be far more involved and inevitably take over Alonso's position who I can imagine hitting one of the 'emerging economies' for a last pay cheque soon - 31 next month after all. He's looked good in the time I've watched him (which is nearly every weekend as I tend to follow Real Madrid's games, much to my enjoyment) and now having been exonerated of most defensive resposibilites can do some serious damage in the final third coupled with their runners.