Is there a correct answer for the "best"? Shouldn't it be "your favorite"?
Anyhow, given the number of lever actions I own, and if I had to pick one, it would not be the one shot the most, but the one most flexible to handle everything asked of it. Another assumption would you would have to be a handloader. Also, it would not necessarily be modern manufacture.
So, the rifle would be either a Winchester Model 88 or Savage 99, just for the flexibility of bullets and calibers. Narrowing down to one caliber, it would have to be a .308. Plenty of loading range and plenty of bullet molds available and excellent cartridge design.
If this question would be asked mid-20th century, I would opt for a Model 94 in .30-30 or .32 Special. If asked this coming December 26th, it would be a .22 lever. If the question was for a current make, it would hands down be a Henry Big Boy Steel in .357.
Edited to add: great thread! Thanks to whoever started it and everyone adding to it!!!