Hands down... Serious Seeds. they have been perfecting the same 5 strains since 1994. I have grown many of their strains with great success. the only one I didnt like was Chronic.
AK-47 was amazing. kalimist and bubblegum were also pretty awesome. I never grew white russian though.
I will say that I was greatly impressed with germination and my ratio of male to female 2-1. no hermies.

Serious doesnt try to come up with the latest hype strain to put in magazines to get attention or increase sales. they have been consistant in their efforts to stabilize the strains they have, and they do an amazing job.
There are many breeders who will cross strains in their basement and sell them on the net, be wary of a companies history and backround before buying their seeds.
there are many different breeders out there who take the job seriously ( no pun intended) but my experience with serious has made me a believer.

Hope this helps.

AK-47, hands down my favorite strain of all time. so yeah I am a little biased.