As a band, The Smiths were nowhere near as influential as REM. REM were the driving force in bringing alternative music to mainstream radio in the U.S. which is a hugely significant moment in the history of popular music and very much changed the musical order from the 90s onwards. The Smiths influence as a band is modest in comparison.
Individually though, Johnny Marr is easily more influential than any single REM member. You’ll struggle to find a 90s UK guitarist that doesn’t cite him as a major inspiration. In fact, you could consider his playing the spark that lit Britpop, an entire genre. If you check any “Greatest Guitarist” list, Marr will often make top 20 whereas Peter Buck often barley limps in to the top 100.
Obviously these lists are just opinion, but it’s unarguable that Johnny Marr is one of the most influential alternative musicians of all time. Likewise, REM as a band.