I think it's an interesting question which is hard to definitely answer. There are 250 million Arabic speakers vs about 183 million speakers of Latin based languages (France, Spain, Portugal, Italy).
Both languages became closely linked with a great religion (Christianity, Islam), although the religious significance of Arabic has probably lasted better down to the present.
The lands conquered by Arabic were already peopled by advanced civilisations that had existed for thousands of years, whereas the lands conquered by Latin were occupied by barbarian tribes at a much lower level of development.
Iran and Turkey have their own languages which were never displaced by Arabic, though one can find a few loan words and religious terms. Likewise Urdu in Pakistan.
Similarly, Germanic and other European languages often have some Latin words in them. In the end it's hard to say which was more significant, since the answer depends when and where we mean. Over all Chinese and Hindustani are probably bigger than them both.