There's nothing wrong with the SCAR-L. It does a bit more damage than the G36C, is a tad less accurate, has a red-dot sight, and is otherwise quite similar to most of the other Spec Ops guns. If you like the red-dot sight of the M4, you'll like the SCAR-L's sight.
The DAO-12 is godly--the only one on the list that's indispensible. Takes a while to reload, yes, and is limited in range (inherent in shotguns), but it's a good one--think Jackhammer or S12K with 5 more shots.
The MP7 and P90 are SMGs. If you like SMGs, you'll like them. If you don't, they're completely unnecessary and you shouldn't waste your unlocks on them. (If you like the Engineer kit but don't like the shotgun, then the MP7 will be a nice change of pace. If you like the AT SMGs, then...why use an unlock to get an SMG that's essentially the same?)