3PT:
pros: cheaper, harder to steal, no one wants to borrow it, you can set work height at waist level to save your back, easily taken to the wood site via tractor, cheap to run (tractor diesel), quieter than most self contained ones, one less engine and hydraulic system to maintain, more compact to store
Tow behind:
pros: you can loan it to friends, easy to move from lot to lot
Neither one will have an advantage over speed, capacity, etc. That is a function of the model you buy (HP and pump capacity).
Most will also tilt up vertical or work horizontal. The 3PT can be raised in the horizontal position. To me, that is probably the single best reason to buy one. You do not get an aching back when you are standing up to split.
If you later decide to get a 3PT splitter, then there will be another set of pros and cons about which type of 3PT.