They are 2 different types of tracks...
The Willow Springs big track will test how big your balls are when it comes to speed, I'm dragging knee at 140mph on my 750 in turn 8, I'll say that since you have a big TLR the BIG track will be easier on you to ride... If you always wanted to ride Willow Springs, Do it! To me it is a one of a kind track!
Streets is a very fun track with tighter stuff, part of the track has been repaved, but the skid pad is a little rough but not bad if you pick some clean lines. The Bowl is a pretty fun part of that track! it has 20 degree banking! being that you have a big TLR you'll get a work out for sure!
Both tracks have elevation changes, Big Willow Springs the elevation change is very noticeable, and plays a big role in the design.
Like some said, do both! Streets and Big Willow Springs are next door to each other, trackdays are ran there all the time, do Streets on a Saturday and then Do the Big Track on Sunday!
Be sure to check out http://www.biketweakers.com/trackcalendar_2009.html
for a date at the track when your ready.