GSR = fully loaded with every option (except leather on the earlier years) and the B18C1 VTEC w/shorter geared transmission and no 3rd window brake light on the coupe/hatchback.

RS/LS/GS = same B18B nonVTEC engine.
GS= basically a fully loaded Integra. almost same options as the GSR but without the engine and with leather.
LS = middle level Integra. cloth seating standard, full power windows/doors/sunroof. 91-97 had hubcaps, 98 had 14" alloys, 99-01 had 15" alloys (same wheels as the 97 GSR).
RS= lowest level Integra. cloth seating standard. not full power (sedans have pwr doorlocks and windows tho). all years have hubcaps standard. side molding and side view mirrors are not body color matched. no sunroof. no cruise control. basically the Integra with the least amount of options from the factory, but as a result, the lightest models of all Integras.

ITR = Integra Type R. B18C5 VTEC. even shorter geared transmission than the GSR. factory LSD. no sunroof. 5lug with slightly lower springs with a stiffer rate and stiffer shocks. factory mounted front lip. no side moldings. better flowing exhaust system. miscellaneous differences in the interior trim.