If you have to ask, you're not ready for it...
Jokes aside, really, Shimano. No question. I have a Lexa, I use it all the time, I like it, but it's still no Shimano.
Now if it was about money (which it doesn't seem to be), and not really a choice between the two, the Lexa has been fine for me. I know of at least 3 people that have had problems with their Lexas, though.