It depends on what you want from the calculations. First, I'll assume that you are mainly interested in calculating the pitch stability of the aircraft to help you determine where to locate the CG.
The tools you've used are fine and you won't gain much from the other tools.
AVL, XFLR5, and VSPAERO use fundamentally similar (though with differences) techniques -- i.e. they basically amount to a thin-surface vortex lattice potential flow code.
DATCOM instead uses a component-wise buildup and other table lookups from classical computations (some may be similar to a VLM) and empirical fits (from test data) to calculate stability derivatives.
XFLR5 is essentially AVL with a boundary layer model added on (like XFoil).
VSPAERO also has a thick-surface mode, but it won't make a big difference for the computations you're after.
VSPAERO has the ability to include an actuator disk or unsteady rotating blade propeller model. If you needed to capture propeller effects, that would be a strong advantage.
VSPAERO has a linearized supersonic mode. VSPAERO has some very limited viscous models. VSPAERO has unsteady modes and other bells and whistles.
DATCOM has results for transonic, supersonic, and hypersonic flows -- it also includes viscous effects.
The most important difference between the tools is how easy it is to build the input model. OpenVSP (I'm admittedly biased) is far and away the easiest here. You can go from nothing to a model and results very quickly.
XFLR5 and AVL have very similar approaches to build the model.
DATCOM is a very different world. If you're using a user-friendly front-end software to DATCOM, it may not be too bad, but if you're classically using the paper copy of DATCOM, it is a laborious process to get a full set of results.
If your aircraft is conventional, all of these are easier. If for example, you're designing a flying wing, then you'll need to be more careful to make sure the lateral-directional effects are captured.
The best place to ask OpenVSP questions is on the OpenVSP Google Group.
