I own both the Litespeed & Houdini and like both. Scratch that....LOVE both.
But the Litespeed is heavier and adds a bit more warmth. Added warmth can be good or a hindrance, depending on conditions. I usually don't look to my windshirt for warmth, per se, so the Houdini usually wins out.
The Houdini is more "no frills", which I like, too.
In contrast to Dave's comment, my Litespeed is longer in the torso than my Houdini (both Large), which I REALLY appreciate.
Add to all this that the Litespeed is my preferred jacket around town and I hopelessly can't get rid of either one!
I can wear my Montbell down inner or my BPL primaloft vest under both windshirts.
My recommending one over the other comes down to this: if you want the lighter of the two with no frills other than the adjustable hood, get the Houdini. If you want slightly warmer with extra length and more refined touches, get the Litespeed.
Sorry so long-winded (I tend to be that way)...hope this helps.