Get the G73 with the 460M. The G73 had issues with the Radeon cards when they were first released earlier in the year. The GeForce is the better card & will havew fewer problems. I have the G72 and I love it. The G73 with the 460M is even better.
The GeForce GTX 460M is the better choice. The benchmarks you are looking at are synthetic and don't completely resemble real world gaming performance. One good example is the memory bus of each card. The 460 has 192 bit while the 5870 has 128 bit. Also (as I stated earlier) if you read the G73 reviews, people were having problems with the Radeon equiped G73s, but few (if any) have reported problems with the GeForce. Both cards are capable performers though and the decision is ultimately yours to make. If it were me though, I'de feel better with the GeForce GTX 460M.