Well that descision is the one only you can make. Your best bet is to look around, and see if you can test drive both. preferably ones that are stock, and ones that have some work done, so you can get a feel for them modded also. I know that not a lot of people can do that, but other then riding both machines back to back, you won't be able to get a solid feel for how they compare to each other.
If you can ride both regardless of mods, I would do so, Just to see how the mannerism's of each bike is, see how they turn, if it's tippy, wheely it a little (if the owner doesn't mind), see if there's anything off camber to ride on see how it likes to side hill, stuff like that.
~Bill