RPTools has an excellent core 'under the covers' so to speak but it looks and feels exactly like what it is - a hobbyist project. Roll20.net has that finish and veneer that only monied projects usually take the time to achieve. $$$cha-ching$$$
Sure Roll20 and Fantasy Grounds *look* better. But feature-wise... they're still significantly behind what MapTools *can* do (getting it to do it is, of course, the hurdle).
These days, it really comes down to this--
1) Out-of-the-box fit and finish.
2) Pre-made and deployable commercial products and assets.
3) Significant out-of-pocket expenses to exploit their strengths.
1) Ridiculous customization options.
2) Best light, sight, and vision blocking available.
Maptool is *still* the Millennium Falcon of VTT's.