Top Speed - So far, most web sites say at best that it goes more than Mach 1.8. However, none would even dare come out and say that it is even Mach 2 capable, meaning that it probably isn't. And we all know that the F-16 (much less) is more than capable of going Mach 2.
Maneuverability - Depends on the speed. At under 450 or 400 miles per hour, the Hornet all day long. However, should the speed rise above that (especially supersonic), the well let's just say the Falcon will be eating Hornet real soon.
Range - F-16XL definitely, cuz I did the math. If the F/A-18 has a range of let's 2,346 kilometers (Navy Fact File - http://www.chinfo.navy.mil/navpalib/factfile/aircraft/air-fa18.html), and I divide that by 1.6 (to change kilometers to miles), and then multiply by 1.4, since the F/A-18 Super Hornet is supposed to have a range that's 40% longer than the F/A-18 Hornet, you get roughly 2,053 miles, while the F-16XL has a range of 2,850 miles, which is obviously greater.
Payload - The F/A-18E/F has two extra hardpoints. The F-16XL has far more, all capable of carrying at the very least a 500 - lb Mk. 82 bomb. You do the math.
Payload diversity & Avionics - I agree with ya here.
Final Note - Heck yeah they should have put the F-16XL into production. It's a heck of a better air - ground fighter than the F-15E, but hey, that's just my opinion.