First, you should check out our Recomendations feature to make sure your fellow ATP members also recommend a particular company. We know the best places to shop!
Second, all 4" pots are not created equal. The conifer on the left is from Park Seeds. In the description, they specify a 4" pot. What they meant was a 3.5" square pot that is 4" deep (These are my measurements, I could not find this info on their website). The conifer on the right is from Stanley & Sons Nursery in Oregon. This is their 4" pot. It is 4" square and 5" deep.
There is a considerable difference between these two pots.