It is a very interesting question, the Gallardo/R8.
Even if the R8 seems a bit better balanced technically speaking, the look of the Gallardo is just incredible...Its name too.
I don't know how they are priced. The V10 R8 will be near the Gallardo I think, and then, I would pick the Lambo in a heartbeat.
The R8 has only interest in V8 version, lower-priced, where it can challenge the 911/Aston.
But it won't.

I don't see it selling a lot, for me the sales will decrease considerably once the "wow, new" instant has passed. It is just an Audi after all, and looks like a stretched TT from certain sides... Nothing to compete with Porsche perfection and Aston's astonishing, stunning look.

So for me, two things are bad flaws: it is just an Audi, and it sort of looks like a TT.