Some things to consider as you work through this decision......
> How many trees are you going to plant each season?
....You shouldn't be planting more than you can harvest in one year. Even though it may take 6-8 yrs to reach cutting size, you may not want to have 2000 trees all at 6' tall at the same time. You need to stagger your planting to align with the harvesting demands.
> Tree spacing?
.....Don't over plant and have no room for your mowers/equipment to traverse between the tree rows. You can plant upwards of 1100 trees per acre with a roughly 6x6 spacing, but do you want to or do you have more room to use to make working on them easier. And remember that once the tree has been cut down, you may have to deal with the remaining stumps and cutoffs. Spaced too tightly and you'll be doing this by hand.
> Species breaks?
.....Don't plant a single species everywhere or all in one location. Break up your planting patterns for variety and growth and disease controls. Most of all don't plant all of one kind together. If for instance you get Spruce rust, it will spread through your whole crop unless you segregate and split the Spruces up by planting white pine; balsams; etc in a patchwork to separate and prevent wholesale spread of possible diseases.
FYI - My 14 yr old son and I plant 600 seedlings (WhitePine and Norway Spruce) over a weekend by using a subsoiler on the tractor for the first pass cuts, and followed up with a dibble bar for hand planting. Yes it was tough but we got through it and got excellent survival rates over this past dry summer. This Spring we'll be planting about another 1000 seedlings (Balsam & Scotch) using a hand held powered auger (Earthquake 2 stroke engine type). We'll see how that goes versus the dibble bars.
If you are planting thousands of seedings and developing a commercial tree farm for mass harvesting, then the tree planter is a must. If you are starting a small operation and want to learn as you go without all the expense, there are other ways to jump in for lower cost and volume.