Keil is definitely the best. However, if you are developing in an environment where the cost of development tools is important, you may want to try Hi-Tech.
I can not give you current numbers, but ~3 years ago I were assigned a comparison between some compilers and found that, compared to Keil, the Hi-Tech compiler used about 3% more memory with a corresponding increase in execution time. Fearing a lawsuit, I shall not give you the numbers for the other compilers I tested.