I absolutely would go for the GSR. The Si is just a toned down GSR, and the Lude is heavier, not as nimble feeling and also more expensive and harder to find parts for down the road if you want to seriously modify the car.

An Integra gives you a good platform to have fun with, even if its stock with a few basic mods. Its quick, agile, looks good, easy to repair, plenty of parts available, etc.