I think their potentials are about the same, 100-pt forward/Franchise D-man. But I would be much more comfortable with JT in our system than JVR, I think he's more of a sure thing and will most likely contribute faster. Taveras is also a much better goalscorer than JVR, while JVR MIGHT have the edge playmaking-wise, but I'm really just going by what I know about them, haven't seen enough of them (I don't judge a player by the WJC's alone like many on this site do). JVR obviously has the size advantage, but until he uses his size to be physical, it limits his effectiveness on the ice.
And considering the Flyers forward/defensive depth, I'd trade JVR for Hedman in an instant, cause it immediately fills the teams need.
So to answer the question, no, I probably would not trade away the 1/2 pick for JVR, just not worth the slighty higher risk that JVR has over JT/Hedman