heres a quick summary, GS,LS,RS the 3 models concinerd the lower models, boasting 142hp dohc b18a/b(a for under94 b for 94+) Gsr comes with 15inch Rims, while ls, rs, gs come with 14 inch hubcaps(some come wiht 14-15 inch rims depending on the original buyer) I dont think there are too many differences between years (except 1st gens which i dont know about) 2nd gens are slightly lighter and have differnt more civic'y body style.
the GSR is the upscale model of the integra. It comes with a 180hp v-tec engine(the hp varies in JDM and USDM models) It comes with all luxury featues of the integra.(including a spoiler)
the last model is the Type-R which is simply teh racing model which has some weight reduction and a more powerful 210hp v-tec engine(b18c5)