A friend of mine has one of those and it is a BIG bike. Not the kind of bike you want to learn to ride on. Plus, if you ride that I doubt you'll ever want to ride a Harley afterward. :sneaky:
Having ridden both large Hondas and Harleys, I still love my Harley. Of course, I also still have my old CB450 and love it too, though it's semi-retired now and on collector vehicle plates.
Given the choice of a VTX 1800 or a Big Twin Harley, I'd take the Harley. Now, if you were talking about a Valkyrie (the original '96-'03 models) instead of a VTX, I'd be inclined to shift to the Honda. It's just that the VTX is just a Harley knock-off. The Valkyrie was its own thing, like the Triumph Rocket III. Of the current Hondas, I'd much prefer a CB1100 over a VTX (and, honestly, even over a Harley) if I were looking for a larger bike.
Harley has some smaller entry level bikes available now in a 500cc and 750cc range but I have zero experience with them. You will learn faster on a smaller, lighter bike.
Cycle World seemed to like Harley's Street 750 and the 500 is about the size that I've always considered to be the perfect beginner bike (I tend to think that the 450-550 range is best for new riders). Still, I don't recommend learning on a new bike.
IMO it's best to start out on an older UJM or, if you're not comfortable with a bike from the 1980s, a Ninja 250 or 500.
ZV