What are we talking about here, a few inches difference in gun grouping? the Mosquito carried out every task asked of it exceptionally well. (Take a look at the old Mossie Vs Ju-88 thread for the full list). The Lightning was a good fighter, but only in the Pacific where Japanese fighters couldn't keep up with it. In Europe, the Mosquito was more effective as a day fighter when used on Ranger intruder sorties over enemy airfields. The Lightning was generally out of its depth against German fighters, especially if they encountered them in any significant numbers.
Also, the Mossie could be, and was, used as a high-speed VIP transport and carrier-borne Anti-shipping strike aircraft (the High-ball version).
As for intercepting, they are very closely matched - having 40 seconds worth of ammo is no use if it takes 10 seconds to bring one down (exaggerated I know, but you know what I mean), so I wouldn't be surprised if both aircraft carried the same 'bombers-worth' of ammunition in their guns.
Oh, and don't knock the Mosquito's
durability - it came back with all sorts of $hit£ done to it.
All in all, I go for the Mosquito - the two are only closely matched in the fighter role. In every other role the Mossie wins (IMHO).