I'll stick by my guns - Both positions do need cover / replacements, but I'm more worried about getting a player to challenge for Scholes's position, than a player to cover/challenge for carricks.
Modric / M'vila / Martinez all seem like good targets, although admittedly I've only watched the former for more than 1-2 games (I watched Europa, so a little of Martinez). M'vila's passing percentage was around 90%+, so I'm sure he can certainly spread the play well, or at least get the simple passes right (Carrick was doing Scholes-esque passes throughout the season, although this got curbed a little when Scholes came back - he let him do those crazy 40 yard crossfield passes), and I'd be happy with any of them, on paper (The litmus test is watching them, obviously!).
With a player more in the mould of Carrick, we do get a player that can play alongside him, as well as covering for Carrick himself, so that is useful. Furthermore, those targets ARE younger.
But in the medium term; the next 4-5 years, I think a Modric player would bode very very well for our fortunes; like having a young Scholes joining the team, and then us supplementing our midfield for a "Carrick" type player next season.
That's my preference, although SAF knows best, and obviously the availability of players will help dictate which type of player he may look to gain more cover for.
Just a small (pedantic) thing; but if we get Clyne, we have cover / replacement for Evra and Rafael, as Clyne can play either full back position (not ideal, but hey. Evra's still great). Also, if we get Powell, and another midfielder say Martinez for example, that's 2 CM's