Is the GA R package the best Genetic Algorithm package?
For such questions, I like to go to the Task Views on CRAN, since the packages noted there are, to a degree, pre-vetted by the R community. I'd trust those a tiny bit more than just googling myself.

The Machine Learning Task View at CRAN says:


  Packages rgp
  and
  rgenoud
  offer optimization routines based on genetic algorithms. The package
  Rmalschains
  implements memetic algorithms with local search chains, which are a
  special type of evolutionary algorithms, combining a steady state
  genetic algorithm with local search for real-valued parameter
  optimization.