Garr, Hanita, Destiny Diamondback, KOR...all great end mills. There is no "best".
If you want great tool life, I can attest to the Destiny Diamondback. We have a repeat job out of 6061 on our Speedio, where I pocket 4" x 4" x 1.25" deep. I've had one of these 1/2" Diamondbacks last over 10,000 parts and only changed it because I was leaving a noobie to run the machine over the weekend and didn't want to take any chances of it failing.
That end mill I run at 16k, 1.25" deep and .100" stepover at 400 IPM. It's a beast.
That being said the Garr Alumastar gives the best finish that I've seen.
Hanita...you can't go wrong.
KOR... I haven't really tested it much but it seems like it's great too.