We present the results of a comparative study of the intra-night optical variability (INOV) characteristics of radio-loud and radio-quiet quasars, which involves a systematic intra-night optical monitoring of seven sets of high luminosity AGNs covering the redshift range z ≃ 0.2 to z ≃ 2.2. The sample, matched in the optical luminosity -- redshift (M_B -- z) plane, consists of seven radio-quiet quasars (RQQs), eight radio lobe-dominated quasars (LDQs), six radio core-dominated quasars (CDQs)

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... five BL Lac objects (BLs). Systematic CCD observations, aided by a careful data analysis procedure, have allowed us to detect INOV with amplitudes as low as 1 single quasar monitored as continuously as possible on a night. Considering cases of only unambiguous detections of INOV we have estimated duty cycles (DCs) of 17 low amplitude and low DC of INOV shown by RQQs compared to BLs can be understood in terms of their having optical synchrotron jets which are modestly misdirected from us. From our fairly extensive dataset, no unambiguous general trend of a correlation between the INOV amplitude and the apparent optical brightness of the quasar is noticed.