I think it's commonly accepted among linguists that Italian is the closest to latin in general, somewhere I've read that it has the highest percentage of latin roots of any Romance language. I've also seen the argument on the 'net that Romanian is grammatically closer. The original home of the language in Latium now located in the Lazio region provinces of Roma and Latina.
Looking at Italian, with my admittedly moderate skill level, and Latin they seem to have the same relationship as Old English just after the Normans and contemporary English. In fact the English model may be instructive, no one doubts the evolution between modern British English and earlier versions of English but apparently there are words used in the American Southern dialect--most whites there were descendents from English/Scots-Irish stock--that keep certain words from that era where the Brits have long ago dropped them from use. In the same sense remember seeing a few words from Spanish, French and Portugese that were descendent from Latin but were replaced in Italian.
I often tell my students that Modern Italian is closer in many ways to the Latin spoken in Rome 2000 years ago than Modern English is to the English spoken in London only 1000 years ago. It's like the Boss said:
Well now everything dies baby that's a fact
But maybe everything that dies someday comes back