Well saskue at this point is his very strong, and is able to add shape manipulation to amaterasu, an ability that itachi was unable to do (at least we never saw him do it), but it appears that itachi specialize more in gen-jutsu than nin-jutsu, being that he"s very skilled and versatile using tsukuyomi and normal gen-justu (he always iniates gen-jutsu as well), you didn't have to look Directly in his eyes, his ring was also a third eye and could also catch you in an illusion. Thus itachi had greater gen-jutsu abilities and saskue have greater nin jutsu abilities.
Now saskue's susanoo is strong indeed, but it is a shell compared to itachi's, itachi's lvl 1 susanoo protected him from a lighting moving at a 1/1000 of second, while two ribs of saskue's susanoo broke from a back slap by raikage. Itachi's lvl 3 susanoo also possessed sword of totsuka and yata mirror items that itachi collected, thus pimping up his susanoo even more.
Both saskue and itachi is good at tai-jutsu, but I give itachi the edge because he is physically faster than saskue, and is able to form hand signs at lighting speed, even when in tai-jutsu combat (he is also able to form signs with one hand). Itachi was also a genius and way more experience than saskue.
in conclusion itachi at full strength (no sickness), pawns saskue 2 folds.