 while processing this directive] [an error occurred while processing this directive]HTOL[an error occurred while processing this directive] vehicles aren't technologically possible today. Today, the competition is beteen [an error occurred while processing this directive]VTOL[an error occurred while processing this directive] [an error occurred while processing this directive]SSTO[an error occurred while processing this directive] designs like [an error occurred while processing this directive]Kankoh-Maru[an error occurred while processing this directive] and New Shepard and two-stage spaceplanes like SpaceShipTwo/White Knight Two. [an error occurred while processing this directive]VTOL[an error occurred while processing this directive] designs have the appeal of a single stage which avoids the engineering issues of in-flight separation. Spaceplanes have the advantage of a large legacy of practical aviation experience to draw on, and an easier fit with existing airport operations and regulations.
Although, in future, new-technology air-breathing rocket engines may come to be used for some part of passenger launch vehicles' flight to orbit, it's difficult to make a convincing case that vehicles using technology that doesn't exist yet will be competitive with ones using known technology for at least the next few decades. Henry Ford didn't wait for the V-8 engine to be invented and developed before he started selling cars!
See Rockets versus Planes for more on this ongoing debate. [an error occurred while processing this directive] [an error occurred while processing this directive]