I looked at the Lude and Civic Si when I got my GSR. The reason I got the GSR was largely to do with the salespeople at Acura. They were a lot less pushy, and much more friendly than the Honda salesman and I actually got the best lease deal on the GSR. The Si was close but I was trading in my girlfriend's (now wife) Civic EX and I wanted something new.
That said I really think I made the best decision and this is almost 4 years later. I love how my GSR is light and nimble. The power is good, the mods plentiful, and the possibilities are endless with the B18C1 engine. I would like an H22A in my wife's Accord though